Automatic tubing lock for ultrasonic sensor interface

ABSTRACT

An ultrasonic air-in-line detection system for use in detecting air bubbles in the fluid line of a disposable cassette mounted on a main pump unit is disclosed which automatically loads the outlet tubing at the bottom of the cassette into a slot in an ultrasonic sensor housing when the cassette is installed on the main pump unit. The system uses a tubing adapter mounted on the outlet tube below the cassette, with the tubing adapter having a tapered top end. The tubing adapter interacts with a pair of ramps located on the bottom and front of the ultrasonic sensor housing around the slot to draw the tubing adapter into a recess located on the bottom of the ultrasonic sensor housing, thereby drawing the outlet tubing fully into the slot between an ultrasonic transmitter and an ultrasonic receiver in the ultrasonic sensor housing when the cassette is installed.

IDENTIFICATION OF RELATED PATENT APPLICATIONS

This application is related to seven other copending patentapplications, all of which were filed on Dec. 1, 1987. These patentapplications are U.S. Ser. No. 127,333, entitled "Disposable Cassettefor a Medication Infusion System," U.S. Ser. No. 127,350, entitled"Piston Cap and Boot Seal for a Medication Infusion System," U.S. Ser.No. 128,122, entitled "Pressure Diaphragm for a Medication InfusionSystem," U.S. Ser. No. 128,009, entitled "Cassette OpticalIdentification Apparatus for a Medication Infusion System," U.S. Ser.No. 128,121, entitled "Air-In-Line Detector for a Medication InfusionSystem," U.S. Ser. No. 127,359, entitled "Cassette Loading and LatchingApparatus for a Medication Infusion System," and U.S. Ser. No. 127,133,entitled "Mechanical Drive System for a Medication Infusion System."

This application is also related to four other filed copending patentapplications, all of which were filed on Dec. 4, 1987. These patentapplications are U.S. Ser. No. 128,973, entitled "Fluid Delivery Controland Monitoring Apparatus for a Medication Infusion System," U.S. Ser.No. 128,966, entitled "Clinical Configuration of Multimode MedicationInfusion System," U.S. Ser. No. 128,978, entitled "User Interface forMedication Infusion System," and U.S. Ser. No. 129,013, entitled"Patient-Side Occlusion Detection System for a Medication InfusionSystem."

This application is also related to three other concurrently filedcopending patent applications. These patent applications are U.S. Ser.No. 07/403,418, entitled "Ultrasonic Transducer Electrical InterfaceAssembly," U.S. Ser. No. 07/403,289, entitled "Ultrasonic Air-In-LineDetector Self Test Technique," and U.S. Ser. No. 07/403,512, entitle"Ultrasonic Air-In-Line Detector for a Medication Infusion System."

BACKGROUND OF THE INVENTION Field of the invention

The present invention relates generally to an ultrasonic system fordetecting the presence of air in a fluid line, and more particularly toan apparatus which automatically loads the outlet tubing at the bottomof a disposable cassette into a notch in an ultrasonic sensor housinglocated on a main pump unit when the cassette is installed on the mainpump unit.

In the past there have been two primary techniques which have been usedto deliver drugs which may not be orally ingested to a patient. Thefirst such technique is through an injection, or shot, using a syringeand needle which delivers a large dosage at relatively infrequentintervals to the patient. This technique is not always satisfactory,particularly when the drug being administered is potentially lethal, hasnegative side effects when delivered in a large dosage, or must bedelivered more or less continuously to achieve the desired therapeuticeffect. This problem results in smaller injections being given at morefrequent intervals, a compromise approach not yielding satisfactoryresults.

Alternatively, the second technique involves administering a continuousflow of medication to the patient, typically through an IV bottle.Medication may also be delivered through an IV system with an injectionbeing made into a complex maze of IV tubes, hoses, and otherparaphernalia. With drop counters being used to meter the amount of bulkfluid delivered, many medications still end up being administered in alarge dosage through an injection into the IV lines, although themedications may be diluted somewhat by the bulk fluid.

As an alternative to these two techniques of administering medication toa patient, the relatively recent addition of medication infusion pumpshas come as a welcome improvement. Medication infusion pumps areutilized to administer drugs to a patient in small, metered doses atfrequent intervals or, alternatively, in the case of some devices, at alow but essentially continuous rate. Infusion pump therapy may beelectronically controlled to deliver precise, metered doses at exactlydetermined intervals, thereby providing a beneficial gradual infusion ofmedication to the patient. In this manner, the infusion pump is able tomimic the natural process whereby chemical balances are maintained moreprecisely by operating on a continuous time basis.

One of the requirements of a medication infusion system is dictated bythe important design consideration of disposability. Since the portionof the device through which medication is pumped must be sterile, inmost applications of modern medication infusion equipment some portionsof the equipment are used only once and then disposed of, typically atregular intervals such as once daily. It is therefore desirable that thefluid pump portion of the infusion pump device be disposable, with thefluid pump being designed as an attachable cassette which is ofinexpensive design, and which is easily installable onto the main pumpunit.

It will be perceived that it is desirable to have a simple disposablecassette design to minimize the cost of construction of the cassette,using the minimum number of parts necessary in the design of thecassette. The design of the cassette must be mass producible, and yetresult in a uniform cassette which is capable of delivering liquidmedication or other therapeutic fluids with a high degree of accuracy.The cassette should include therein more than just a fluid pump; otherfeatures which have formerly been included in peripheral devices may beincluded in the cassette.

Such a system has been disclosed in all of the above-identifiedpreviously filed related applications. Of these applications, U.S. Ser.No. 128,121, entitled "Air-In-Line Detector for a Medication InfusionSystem," is hereby incorporated herein by reference.

An essential function of a medication infusion system is to avoid theinfusion of fluid containing more than a minimal amount of air bubblestherein. Although steps may be taken to minimize the possibility of airbubbles being contained in a fluid which is to be infused to a patient,it is essential to monitor the fluid line before it reaches the patientto ensure that air bubbles remain in the fluid which is to be infusedare detected. The detection of air bubbles in all fluids which are to beinfused is therefore a critical design requirement.

One type of air-in-line detector which has been used in the past is anultrasonic detector, which places an ultrasonic transmitter on one sideof a fluid line and an ultrasonic receiver on the other side of thefluid line. Fluid is a good conductor of ultrasonic energy while air orfoam is not. Accordingly, if there is an air bubble in the fluid linebetween the transmitter and the receiver, the signal strength will begreatly attenuated, and the presence of the bubble will be indicated.Examples of ultrasonic air-in-line detectors include U.S. Pat. No.4,764,166, to Spani, and U.S. Pat. No. 4,821,558, to Pastrone et al.

The Pastrone et al. device has a projection from a disposable cassettewhich fits into an ultrasonic detector. Thus, the fluid path monitoredin the Pastrone et al. device is within the fluid cassette. It isparticularly desirable to monitor the fluid path as it leaves thecassette to determine whether or not there are air bubbles containedtherein. The Spani device is designed to monitor fluid flow through asegment of flexible tubing, which tubing may be the fluid path as itleaves the cassette.

The Spani device will work quite well to detect the presence of airbubbles in the tubing, but is had at least two disadvantages in itsoperation. First, the tubing must be installed in the Spani device in astep additional to the installation of a cassette onto a main pump unit.In other words, there is no provision in Spani for the tubing toautomatically be installed in the Spani device. This represents adisadvantage since an extra step is required by the operator of thesystem.

Secondly, the Spani device is extremely sensitive to placement of thetubing in the sensor. If the tubing is moved slightly, the path ofultrasonic energy could be disrupted, resulting in a false indicationthat there is air in the fluid line. Other than friction, there is noprovision in the Spani device to retain the tubing in place in thesensor. Thus, while the Spani sensor operates well, it has certaindisadvantages with regard to the installation and retention of thetubing in the sensor.

It is therefore the primary objective of the present invention toprovide an ultrasonic air-in-line detection sensor for use with theoutlet tubing from a cassette, with the tubing being automaticallyloaded into the proper position in the sensor when the cassette isinstalled on a main pump unit. The system of the present inventionshould thus load the tubing into the sensor, in the proper position,with no more effort required than the effort to load the cassette itselfonto the main pump unit. It must be emphasized that the tubing has to beloaded correctly into the sensor in a highly repeatable manner.

It is also an objective that once the tubing has been properly loadedinto the sensor that it be retained in the sensor in a manner making ithighly unlikely that the tubing will be able to move with respect to thesensor. The tubing must thus be both properly loaded initially into thesensor, and retained in its proper position in the sensor to preventfalse signals due to movement of the tubing in the sensor. In addition,it is an objective that the tubing be automatically removed from thesensor when the cassette is removed from the main pump unit withoutrequiring any additional steps to be performed.

Despite the inclusion of all of the aforesaid features, the system ofthe present invention shall utilize a minimum number of parts, all ofwhich parts are of inexpensive construction, yet which afford theassembled sensor and its mounting hardware the high degree of accuracywhich must be retained. The system of the present invention must also beof a design which enables it to compete economically with knowncompeting systems, and it must provide an ease of use rivaling the bestof competing systems. The system must accomplish all these objects in amanner which will retain and enhance all of the advantages ofreliability, durability, and safety of operation. The system of thepresent invention must provide all of these advantages and overcome thelimitations of the background art without incurring any relativedisadvantage.

SUMMARY OF THE INVENTION

The disadvantages and limitations of the background art discussed aboveare overcome by the present invention. With this invention, anultrasonic transmitter and an ultrasonic receiver are mounted in anultrasonic sensor housing mounted below the position in which adisposable cassette will be mounted on a main pump unit. A notch isformed in the front of the ultrasonic sensor housing to receive theoutlet tubing, which extends from the bottom of the cassette. Theultrasonic transmitter is located in the ultrasonic sensor housing onone side of the notch, and the ultrasonic receiver is located in theultrasonic sensor housing on the other side of the notch.

A recessed area is located on the bottom of the ultrasonic sensorhousing around the notch. Two inclined ramps are located on the bottomand in the front of the ultrasonic sensor housing on each side of thenotch, with the ramps being inclined toward the recessed area in thebottom of the ultrasonic sensor housing. A tubing adapter is mounted onthe outlet tubing below the cassette. The tubing adapter is a hollowcylinder with a tapered top end and a flange located below the taperedend.

When the cassette is positioned in front of the main pump unit prior toinstallation, the outlet tubing between the bottom of the cassette andthe tubing adapter is positioned in front of the notch in the ultrasonicsensor housing. As the cassette is installed onto the main pump unit,the outlet tubing between the bottom of the cassette and the tubingadapter will move into the notch in the ultrasonic sensor housing.Simultaneously, the tapered end of the tubing adapter will fit on thebottom of the ramps on the ultrasonic sensor housing.

As the cassette is moved into its final position on the main pump unit,the tapered end of the tubing adapter will slide on the ramps on theultrasonic sensor housing into the recessed area on the bottom of theultrasonic sensor housing. This will pull the outlet tubing between thebottom of the cassette and the tubing adapter fully into the notch inthe ultrasonic sensor housing, orienting it directly between theultrasonic transmitter and the ultrasonic receiver in the ultrasonicsensor housing.

Since the cassette is secured to the main pump unit, and the tubingadapter is located in the recessed area on the bottom of the ultrasonicsensor housing, the outlet tubing between the bottom of the cassette andthe tubing adapter will be retained in the proper position as long asthe cassette is locked into the main pump unit. This ensures both properplacement and retention of the portion of the outlet tubing between thebottom of the cassette and the tubing adapter with respect to theultrasonic transmitter and receiver. Thus, both installation and removalof the tubing into the ultrasonic sensor require only manipulation ofthe cassette.

It may therefore be appreciated that the present invention provides anultrasonic air-in-line detection sensor for use with the outlet tubingfrom a cassette in which the tubing is automatically loaded into theproper position in the sensor when the cassette is installed on a mainpump unit. The system of the present invention thus loads the tubinginto the sensor, in the proper position, with no more effort requiredthan the effort to load the cassette itself onto the main pump unit. Thetubing is thereby loaded correctly into the sensor in a highlyrepeatable manner whenever the cassette is installed.

Once the tubing has been properly loaded into the sensor, it is retainedin the sensor in a manner making it impossible for the tubing to movewith respect to the sensor. The tubing is thus both properly loadedinitially into the sensor, and retained in its proper position in thesensor to prevent false signals due to movement of the tubing in thesensor. In addition, the tubing is automatically removed from the sensorwhen the cassette is removed from the main pump unit without requiringany additional steps to be performed.

Despite the inclusion of all of the aforesaid features, the system ofthe present invention utilizes a minimum number of parts, all of whichparts are of inexpensive construction, yet which afford the assembledcassette a high degree of accuracy. The system of the present inventionis therefore of a design which enables it to compete economically withknown competing systems, and it provides an ease of use rivaling thebest of competing systems. The system accomplishes all these objects ina manner which retains and enhances the advantages of reliability,durability, and safety of operation. The system of the present inventionprovides these advantages and overcome the limitations of the backgroundart without incurring any relative disadvantage whatsoever.

DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiment a uniformdirectional system is used in which front, back, top, bottom, left, andright are indicated with respect to the operating position of thecassette and main pump unit when viewed from the front of the main pumpunit. These and other advantages of the present invention are bestunderstood with reference to the drawings, in which:

FIG. 1 is a top plan view of a disposable cassette body showing most ofthe fluid path through the cassette;

FIG. 2 is a front side view of the cassette body shown in FIG. 1;

FIG. 3 is a back side view of the cassette body shown in FIGS. 1 and 2;

FIG. 4 is a bottom view of the cassette body shown in FIGS. 1 through 3;

FIG. 5 is a right side view of the cassette body shown in FIGS. 1through 4;

FIG. 6 is a left side view of the cassette body shown in FIGS. 1 through5;

FIG. 7 is a partially cutaway view from the front side of the cassettebody shown in FIGS. 1 through 6, showing the bubble trap used to removeair bubbles from the fluid supplied to the cassette;

FIG. 8 is a partially cutaway view from the right side of the cassettebody shown in FIGS. 1 through 6, showing the cylinder of the fluid pumpcontained in the cassette;

FIG. 9 is a top plan view of a valve diaphragm used to seal thepassageways on the top surface of the cassette body shown in FIG. 1, tofunction as the pressure diaphragm, and also to function as the valvesfor the pump;

FIG. 10 is a bottom view of the valve diaphragm shown in FIG. 9;

FIG. 11 is a cutaway view from the back side of the valve diaphragmshown in FIGS. 9 and 10;

FIG. 12 is a cutaway view from the right side of the valve diaphragmshown in FIGS. 9 and 10;

FIG. 13 is a top plan view of a valve diaphragm retainer used to retainthe valve diaphragm shown in FIGS. 9 through 12;

FIG. 14 is a bottom view of the valve diaphragm retainer shown in FIG.13;

FIG. 15 is a back side view of the valve diaphragm retainer shown inFIGS. 13 and 14;

FIG. 16 is a front side view of the valve diaphragm retainer shown inFIGS. 13 through 15;

FIG. 17 is a right side view of the valve diaphragm retainer shown inFIGS. 13 through 16;

FIG. 18 is a left side view of the valve diaphragm retainer shown inFIGS. 13 through 17;

FIG. 19 is a cutaway view from the front side of the valve diaphragmretainer shown in FIGS. 13 through 18;

FIG. 20 is a cutaway view from the left side of the valve diaphragmretainer shown in FIGS. 13 through 19;

FIG. 21 is a cutaway view from the right side of the valve diaphragmretainer shown in FIGS. 13 through 20;

FIG. 22 is a top view of a bubble chamber cap;

FIG. 23 is a bottom view of the bubble chamber cap shown in FIG. 22;

FIG. 24 is a left side view of the bubble chamber cap shown in FIGS. 22and 23;

FIG. 25 is a cutaway view from the back side of the bubble chamber capshown in FIGS. 22 through 24;

FIG. 26 is a cutaway view from the right side of the bubble chamber capshown in FIGS. 22 through 24;

FIG. 27 is a top plan view of a slide latch used both to lock thecassette in place on a main pump unit, and to pinch off the IV outletline prior to installation on the main pump unit;

FIG. 28 is a right side view of the slide latch shown in FIG. 27;

FIG. 29 is a bottom view of the slide latch shown in FIGS. 27 and 28;

FIG. 30 is a back side view of the slide latch shown in FIGS. 27 through29;

FIG. 31 is a front side view of the slide latch shown in FIGS. 27through 30;

FIG. 32 is a cutaway view from the left side of the slide latch shown inFIGS. 27 through 31;

FIG. 33 is a side plan view of the piston cap and boot seal, whichfunction both as a piston and as a bacterial seal;

FIG. 34 is a top end view of the piston cap and boot seal shown in FIG.33;

FIG. 35 is a bottom end view of the piston cap and boot seal shown inFIGS. 33 and 34;

FIG. 36 is a cutaway view from the side of the piston cap and boot sealshown in FIGS. 33 through 35;

FIG. 37 is a back side plan view of a piston for insertion into thepiston cap and boot seal shown in FIGS. 33 through 36;

FIG. 38 is a front side view of the piston shown in FIG. 37;

FIG. 39 is a top view of the piston shown in FIGS. 37 and 38;

FIG. 40 is a left side view of the piston shown in FIGS. 37 through 39;

FIG. 41 is a bottom view of the piston shown in FIGS. 37 through 40;

FIG. 42 is a cutaway view from the right side of the piston shown inFIGS. 37 through 41;

FIG. 43 is a perspective top view of a tubing adapter for installationin the outlet tube below the slide latch;

FIG. 44 is a cutaway view of the tubing adapter shown in FIG. 43;

FIG. 45 is a perspective top view of an assembled cassette using thecomponents shown in FIGS. 1 through 44, with the slide latch in theopened position;

FIG. 46 is a bottom view of the assembled cassette shown in FIG. 45,with the tubing adapter removed for clarity and the slide latch in theopened position;

FIG. 47 is a perspective top view of the assembled cassette shown inFIGS. 45 and 46, with the slide latch in the closed position;

FIG. 48 is a bottom view of the assembled cassette shown in FIGS. 45through 47, with the tubing adapter removed for clarity and the slidelatch in the closed position;

FIG. 49 is a left side view of the latch head used to capture andactuate the piston;

FIG. 50 is a right side view of the latch head shown in FIG. 49;

FIG. 51 is a bottom view of the latch head shown in FIGS. 49 and 50;

FIG. 52 is a top view of the latch head shown in FIGS. 49 through 51;

FIG. 53 is a cutaway view from the right side of the latch head shown inFIGS. 49 through 52;

FIG. 54 is a right side view of the spring retainer to be mounted in thelatch head shown in FIGS. 49 through 52;

FIG. 55 is a front view of the spring retainer shown in FIG. 54;

FIG. 56 is a left side view of the latch jaw to be mounted on the latchhead shown in FIGS. 49 through 52;

FIG. 57 is a bottom view of the latch jaw shown in FIG. 56;

FIG. 58 is a back view of the latch jaw shown in FIGS. 56 and 57;

FIG. 59 is a left side view of the jaws assembly in the open position,the jaws assembly being made up of the latch head shown in FIGS. 49through 52, the spring retainer shown in FIGS. 54 and 55, the latch jawshown in FIGS. 56 through 58, a latch spring, and pins used to assemblethe various components together;

FIG. 60 is a bottom view of the jaws assembly shown in FIG. 59, with thejaws assembly being shown in the open position;

FIG. 61 is a left side view of the jaws assembly shown in FIGS. 59 and60, with the jaws assembly being shown in the closed position (and inthe open position in phantom lines);

FIG. 62 is a bottom plan view of the main pump unit chassis;

FIG. 63 is a front view of the main pump unit chassis shown in FIG. 62;

FIG. 64 is a top view of the main pump unit chassis shown in FIGS. 62and 63;

FIG. 65 is a back view of the main pump unit chassis shown in FIGS. 62through 64;

FIG. 66 is a perspective top view of the cassette guide used to positionthe cassette of FIGS. 45 through 48 on the main pump unit;

FIG. 67 is a sectional view of the cassette guide shown in FIG. 66;

FIG. 68 is a top view of the cassette guide shown in FIGS. 66 and 67;

FIG. 69 is a bottom view of the cassette guide shown in FIGS. 66 through68;

FIG. 70 is a left side plan view of the pump shaft on which is mountedthe jaws assembly shown in FIGS. 59 through 61;

FIG. 71 is a right side view plan view of the slide look used to retainthe cassette shown in FIGS. 43 through 48 in position on the main pumpunit;

FIG. 72 is a bottom view of the slide lock shown in FIG. 71;

FIG. 73 is left side view of the slide lock shown in FIGS. 71 and 72,showing the bevel used to reflect the light beam from the optical lightsource away from the optical light sensor when the slide lock is in theopen position;

FIG. 74 is a top view of the slide lock shown in FIGS. 71 through 73,showing the reflective surface used to reflect the light beam from theoptical light source to the optical light sensor when the slide lock isin the closed position;

FIG. 75 is a front side view of the slide lock shown in FIGS. 71 through74;

FIG. 76 is a back side view of the slide lock shown in FIGS. 71 through75, showing the slanted surface used to reflect the light beam away fromthe corresponding sensor when the slide lock is in the open position;

FIG. 77 is a perspective top view of the upper sensor housing;

FIG. 78 is a sectional view of the upper sensor housing shown in FIG.77;

FIG. 79 is a top view of the upper sensor housing shown in FIGS. 77 and78;

FIG. 80 is a bottom view of the upper sensor housing shown in FIGS. 77through 79;

FIG. 81 is a perspective top view of the lower sensor housing;

FIG. 82 is a sectional view of the lower sensor housing shown in FIG.81;

FIG. 83 is a sectional bottom view of the lower sensor housing shown inFIGS. 81 and 82;

FIG. 83A is a bottom plan view of the lower sensor housing shown inFIGS. 81 through 83;

FIG. 84 is a plan view of a portion of a flex circuit used toelectrically interface with a pair of ultrasonic transducers;

FIG. 85 is a partially exploded perspective view showing how theultrasonic transducers are attached to the flex circuit using conductivetransfer tape;

FIG. 85A is a partially exploded perspective view showing an alternateembodiment in which portions of the flex circuit and the conductivetransfer tape on the back sides of the ultrasonic transducers haveapertures therethrough;

FIG. 86 is a perspective bottom view showing the assembly of FIG. 85installed in the upper sensor housing;

FIG. 87 is a perspective bottom view showing a miniature circuit boardinstalled on the flex circuit of the assembly of FIG. 86;

FIG. 88 is a front plan view of an optical sensor module;

FIG. 89 is a side view of the optical sensor module shown in FIG. 88;

FIG. 90 is top view of the optical sensor module shown in FIGS. 88 and89;

FIG. 91 is a side plan view of a valve actuator;

FIG. 92 is an side edge view of the valve actuator shown in FIG. 91;

FIG. 93 is a bottom view of the valve actuator shown in FIGS. 91 and 92;

FIG. 94 is a top view of one of the actuator guides used to guide andretain in position the valve actuators for one cassette;

FIG. 95 is a side view of the actuator guide shown in FIG. 94;

FIG. 96 is a top plan view of a pressure transducer;

FIG. 97 is a side view of the pressure transducer shown in FIG. 96;

FIG. 98 is a bottom view of the pressure transducer shown in FIGS. 96and 97;

FIG. 99 is a bottom plan view of the elastomeric valve actuator sealused to bias the valve actuators in an upward position;

FIG. 100 is a cutaway view of the valve actuator seal shown in FIG. 99;

FIG. 101 is a perspective view of the main pump unit chassis having thevarious components for one pump mounted thereon;

FIG. 102 is a bottom view of the main pump unit chassis having thevarious components for one pump mounted thereon, with the slide lock inthe open position ready to receive a cassette;

FIG. 103 is a bottom view of the main pump unit chassis shown in FIG.102, with the slide lock in the closed position as it would be if acassette were installed and latched onto the main pump unit;

FIG. 104 is a side view illustrating a cassette in position to beinstalled on the main pump unit;

FIG. 105 is a side view illustrating the cassette as it is engaging themain pump unit, showing the tubing adapter engaging the flared recess inthe bottom of the sensor housing to draw the outlet tube into engagementbetween the ultrasonic transducers;

FIG. 106 is a side view illustrating the cassette fully installed on themain pump unit with the slide latch closed and the outlet tube in fullengagement between the ultrasonic transducers in the sensor housing;

FIG. 107 is a functional schematic diagram of the entire operatingsystem of the infusion pump of the present invention, showing theultrasonic air-in-line detector system and self test therefor;

FIG. 108 is a schematic diagram of the transmitting circuitry for theultrasonic air-in-line detector system for all three channels;

FIG. 109 is a functional schematic diagram of the receiver circuitry forone channel, the circuitry having an output signal;

FIG. 110 is a schematic diagram of the processing circuitry used toprocess the output signal from the receiver circuitry to produce an AILDOutput signal for each channel and an interrupt signal indicating achange in state of the AILD Output signal of one of the three channels;

FIG. 111 shows various waveforms generated by the circuitry of FIGS.108, 109, and 110;

FIG. 112 is a simplified flow diagram illustrating the operation of theair-in-line detector monitoring system; and

FIG. 113 is a simplified flow diagram illustrating the operation of theair-in-line detector self test system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The Cassette

The preferred embodiment of the cassette using the air-in-line detectorof the present invention includes all of the features described above ina single compact disposable cassette constructed of seven parts. Priorto a discussion of the construction and operation of the cassette, thebasic construction of which is the subject of the above-identifiedpatent application entitled "Disposable Cassette for a MedicationInfusion System," it is advantageous to discuss the construction andconfiguration of the seven components included in the cassette. Thefirst of these components and the one around which the other sixcomponents are assembled is a cassette body 100, which is shown in FIGS.1 through 8. The cassette body 100 has an upper surface portion 102which is essentially flat with a number of protrusions and indentationslocated in the top surface thereof (FIG. 1). The upper surface portion102 has a thickness sufficient to accommodate the indentations mentionedabove, some of which are fluid passageways which will be discussedbelow.

Referring generally to FIGS. 1 through 8, a bubble trap 104 is locatedat the front right corner of the cassette body 100 below the uppersurface portion 102, which bubble trap 104 is essentially square incross-section (FIG. 4). The bubble trap 104 includes therein a bubblechamber 106 which is open at the bottom thereof (FIGS. 4, 7, and 8) andclosed at the top by the bottom of the upper surface portion 102 of thecassette body 100. A siphon tube 108 is located in the bubble chamber106, and the siphon tube 108 has an aperture 110 therein leading fromthe bottom of the bubble chamber 106 to the top of the upper surfaceportion 102 of the cassette body 100.

Located behind the bubble trap 104 below the upper surface portion 102of the cassette body 100 on the right side thereof is a pump cylinder112 (FIG. 3-5, 8). The pump cylinder 112 does not extend downward as faras does the bubble trap 104. The pump cylinder 112 is open on the bottomthereof, and is arranged and configured to receive a piston which willbe discussed below. The inner configuration of the pump cylinder 112 hasa main diameter bore 114, with a greater diameter bore 116 near thebottom of the pump cylinder 112. The interior of the bottom of the pumpcylinder 112 below the greater diameter bore 116 as well as the areaimmediately between the greater diameter bore 116 and the main diameterbore 114 are tapered to facilitate entry of the piston. The maindiameter bore 114 terminates at the top thereof in a frustroconicalsmaller diameter aperture 118 leading to the top of the upper surfaceportion 102 of the cassette body 100 (FIG. 1). The smaller diameteraperture 118 is tapered, having a smaller diameter at the top thereofthan at the bottom.

Extending from on the back side of the exterior of the bubble trap 104facing the pump cylinder 112 are two piston retaining fingers 120 and122 (FIGS. 3 and 4) defining slots therein. The slots defined by the twopiston retaining fingers 120 and 122 face each other, and are open atthe bottoms thereof to accept in a sliding fashion a flat segmentfitting between the two piston retaining fingers 120 and 122. The twopiston retaining fingers 120 and 122 extend from the loWer surface ofthe upper surface portion 102 of the cassette body 100 to a locationbetween the bottom of the pump cylinder 112 and the bottom of the bubbletrap 104.

Also extending from the bottom side of the upper surface portion 102 ofthe cassette body 100 are two latch supporting fingers 124 and 126(FIGS. 1-4 and 7). The latch supporting finger 124 extends downwardlyfrom the left side of the bottom of the upper surface portion 102 of thecassette body 100, and at the bottom extends toward the right slightlyto form an L-shape in cross section. The latch supporting finger 124extends toward the front of the cassette body 100 further than does theupper surface portion 102 of the cassette body 100 (FIG. 1), andterminates approximately two-thirds of the toward the back of the uppersurface portion 102 of the cassette body 100.

The latch supporting finger 126 extends downwardly from the bottom ofthe upper surface portion 102 of the cassette body 100 at with the leftside of the bubble trap 104 forming a portion of the latch supportingfinger 126. The latch supporting finger 126 extends toward the leftslightly at the bottom thereof to form a backwards L-shape in crosssection. The latch supporting finger 126 parallels the latch supportingfinger 124, and is equally deep (FIG. 4). The latch supporting fingers124 and 126 together will hold the slide latch, to be described below.

The passageways located in the top of the upper surface portion 102 ofthe cassette body 100 may now be described with primary reference toFIG. 1. The passageways in the top of the upper surface portion 102 areall open on the top side of the upper surface portion 102, and aregenerally U-shaped as they are recessed into the top of the uppersurface portion 102. A first passageway 128 communicates with theaperture 110 in the siphon tube 108 of the bubble trap 104 at one endthereof, and extends toward the back of the upper surface portion 102 ofthe cassette body 100 to a location to the right of the smaller diameteraperture 118 of the pump cylinder 112.

A cylindrical pressure plateau 130 which is essentially circular asviewed from the top extends above the upper surface portion 102 of thecassette body 100 slightly left of the center thereof (best shown inFIGS. 1 through 3, also shown in FIGS. 5 through 8). The top of thepressure plateau 130 is flat, with a channel 132 extending across theflat top of the pressure plateau 130. The channel 132 extends from fiveo'clock to eleven o'clock as viewed from the top in FIG. 1, with theback of the cassette body 100 being twelve o'clock. The channel 132 isalso shown in cross-section in FIG. 115, and in a cutaway view in FIG.116. The depth of the channel 132 in the surface of the pressure plateau130 is not quite the height of the pressure plateau 130 above the uppersurface portion 102 of the cassette body 100, with the channel 132gradually becoming deeper with a smooth transition at the edges of thepressure plateau 130 to extend into the upper surface portion 102 of thecassette body 100 (FIG. 116).

A second passageway 134 in the top of the upper surface portion 102 ofthe cassette body 100 begins at a location to the left of the smallerdiameter aperture 118 of the pump cylinder 112, and extends toward thefront of the upper surface portion 102 approximately above the latchsupporting finger 126. The second passageway 134 then travels to theleft to connect in fluid communication with the end of the channel 132in the pressure plateau 130 located at five o'clock. A third passageway136 in the top of the upper surface portion 102 of the cassette body 100begins at the end of the channel 132 in the pressure plateau 130 locatedat eleven o'clock, and moves toward the back and left of the cassettebody 100.

At the end of the third passageway 136 is a recessed lens portion 138,which recessed lens portion is used to focus and reflect light used todetect air bubbles passing in front of the recessed lens portion 138.The recessed lens portion 138 is also recessed into the top of the uppersurface portion 102 of the cassette body 100 to allow fluid to passtherethrough. The recessed lens portion 138 is part of the apparatuswhich is the subject of the present invention. A fourth passageway 140in the top of the upper surface portion 102 of the cassette body 100begins at the other side of the recessed lens portion 138 from the thirdpassageway 136, and extends from the left and back of the cassette body100 toward the front and right of the cassette body 100 around thepressure plateau 130 to a location at approximately seven o'clock on thepressure plateau 130. It should be noted that the fourth passageway 140is spaced away from the pressure plateau 130 to allow for sealing meanstherebetween.

The end of the fourth passageway 140 terminates at the location at seveno'clock to the pressure plateau 130 in an aperture 142 extending throughthe upper surface portion 102 of the cassette body 100 (FIG. 1). Locatedunderneath the upper surface portion 102 of the cassette body 100concentrically around the aperture 142 is an the outlet tube mountingcylinder 144 (FIGS. 3 and 4) which is in fluid communication with theaperture 142. The outlet tube mounting cylinder 144 extends downwardlyfrom the bottom of the upper surface portion 102 of the cassette body100 to a location above the portions of the latch supporting finger 124and the latch supporting finger 126 extending parallel to the uppersurface 102 of the cassette body 100. A support fin 145 extends to theright from the front of 10 the outlet tube mounting cylinder 144.

Located on top of the upper surface 102 of the cassette body 100 is aslightly raised border 146 (FIG. 1) which completely surrounds the firstpassageway 128, the smaller diameter aperture 118, the second passageway134, the pressure plateau 130, the third passageway 136, the recessedlens portion 138, the recessed lens portion 138, and the fourthpassageway 140. The slightly raised border 146, which is used forsealing purposes, closely surrounds the edges of all of theaforementioned segments of the cassette body 100, except as follows. Theslightly raised border 146 is spaced away from the portions of the firstpassageway 128 and the second passageway 134 adjacent the smallerdiameter aperture 118, and the smaller diameter aperture 118.

The portions of the slightly raised border 146 around the smallerdiameter aperture 118 resembles a rectangle with its wider sides locatedto the front and back and spaced away from the valve diaphragm 170, andits narrower sides to the right of the portion of the first passageway128 adjacent the smaller diameter aperture 118 and to the left of theportion of the second passageway 134 adjacent the smaller diameteraperture 118. The rectangle is broken only at the locations the firstpassageway 128 and the second passageway 134 extend towards the front ofthe cassette body 100.

The slightly raised border 146 has a segment 147 located between theportion of the first passageway 128 adjacent the smaller diameteraperture 118 and the smaller diameter aperture 118 itself, with thesegment 147 extending between the two wider sides of the rectangle. Theslightly raised border 146 also has another segment 149 located betweenthe portion of the second passageway 134 adjacent the smaller diameteraperture 118 and the smaller diameter aperture 118 itself, with thesegment 149 extending between the two wider sides of the rectangle. Theslightly raised border 146 is also spaced away from the sides of thepressure plateau 130, and the portions of the second passageway 134 andthe third passageway 136 immediately adjacent the pressure plateau 130.

Located at the back of the upper surface 102 of the cassette body 100are three cassette identifying indicia 148, 150, and 152. The first andthird cassette identifying indicia 148 and 152 are small, solidcylinders extending upward from the top of the upper surface 102 of thecassette body 100 (FIGS. 1 and 3). The second cassette identifyingindicia 150 is a prism cut into the bottom of the upper surface 102 ofthe cassette body 100 (FIG. 4). The first, second, and third cassetteidentifying indicia 148, 150, and 152 are the subject of theabove-identified patent application entitled "Cassette OpticalIdentification Apparatus for a Medication Infusion System." It will benoted that the cassette identifying indicia 148, 150, and 152 may be inany order or configuration, and are used for different ID codes toidentify up to eight different cassettes. Additional ID bits could alsobe used if more than eight different cassettes are used. If redundantcodes are desired, the three bits would of course accommodate the use ofless than eight different cassettes.

Completing the construction of the cassette body 100 are five hollowcylinders 154, 156, 158, 160 and 162 protruding from the top surface ofthe upper surface 102 of the cassette body 100, an aperture 161 and aslot 164 located in the top surface of the upper surface 102 of thecassette body 100, and a slot 166 located in the top surface of thelatch supporting finger 124. Four of the hollow cylinders 154, 156, 158,and 160 are located around the pressure plateau 130, with the fifthhollow cylinder 162 being located to the left of the aperture 110 overthe bubble trap 104. The aperture 161 is located in the top surface ofthe upper surface 102 of the cassette body 100 in front and to the rightof center of the pressure plateau 130. The slot 164 is located in thetop surface of the upper surface 102 of the cassette body 100 near theback and the right side thereof. The slot 166 is located in the topsurface of the latch supporting finger 124 near the front of thecassette body 100.

Referring now to FIGS. 9 through 12, a valve diaphragm 170 is shownwhich is arranged and configured to fit over the top of the uppersurface 102 of the cassette body 100 (FIG. 1). The valve diaphragm 170is made of flexible, resilient material, such as a medical gradesilicone rubber. The hardness of the material used for the valvediaphragm 170 would be between thirty and fifty on the Shore A scale,with the preferred embodiment utilizing a hardness of approximatelythirty-five. The valve diaphragm 170 has three primary functions, thefirst of which is to seal the tops of the first, second, third, andfourth passageways 128, 134, 136, and 140, respectively. Accordingly,the main surface of the valve diaphragm 170 is flat, and is sized to fitover the first, second, third, and fourth passageways 128, 134, 136, and140, respectively, and also over the entire slightly raised border 146.The flat portion of the valve diaphragm 170 has three apertures 172,174, and 176, and a notch 175 therein to accommodate the hollowcylinders 156, 160, and 162 and a pin fitting into the aperture 161(FIG. 1), respectively, and to align the valve diaphragm 170 in positionover the top of the upper surface 102 of the cassette body 100. Itshould be noted that the valve diaphragm 170 does not necessarilysurround the other two hollow cylinders 154 and 158.

The second primary function of the valve diaphragm 170 is to provideboth an inlet valve between the first passageway 128 and the smallerdiameter aperture 118 leading to the pump cylinder 112, and to providean outlet valve between the smaller diameter aperture 118 leading to thepump cylinder 112 and the second passageway 134. To fulfill thisfunction the valve diaphragm 170 has an essentially rectangular domedportion 178 (shown in plan view in FIGS. 9 and 10, and incross-sectional views in FIGS. 11 and 12) forming a cavity 180 in thebottom of the valve diaphragm 170. When the valve diaphragm 170 isinstalled in position on the top of the upper surface 102 of thecassette body 100, the cavity 180 will be located just inside therectangular portion of the slightly raised border 146 around the smallerdiameter aperture 118 leading to the pump cylinder 112 (FIG. 1).

The cavity 180 will therefore be in fluid communication with the firstpassageway 128, the smaller diameter aperture 118 leading to the pumpcylinder 112, and the second passageway 134. Prior to installation ofthe cassette onto the main pump unit, the cavity 180 allows the openfluid path to facilitate priming of the cassette, where all air isremoved from the system. Once primed, the cassette may be inserted ontothe main pump unit and the cavity 180 will contact valve actuators toprevent free flow through the cassette. By using an inlet valve actuatorto force the domed portion 178 over the segment 147 of the slightlyraised border 146 (FIG. 1), the flow of fluids between the firstpassageway 128 and the smaller diameter aperture 118 will be blocked,but the flow of fluids between the smaller diameter aperture 118 and thesecond passageway 134 will be unaffected. Likewise, by using an outletvalve actuator to force the domed portion 178 over the segment 149 ofthe slightly raised border 146 (FIG. 1), the flow of fluids between thesmaller diameter aperture 118 and the second passageway 134 will beblocked, but the flow of fluids between the first passageway 128 and thesmaller diameter aperture 118 will be unaffected. Extending around andspaced away from the front and sides of the domed portion 178 on the topsurface of the valve diaphragm 170 is a U-shaped raised rib 181, thelegs of which extend to the back of the valve diaphragm 170 (FIG. 9).

The third primary function of the valve diaphragm 170 is to provide apressure diaphragm which may be used to monitor outlet fluid pressure.Accordingly, the valve diaphragm 170 has a pressure diaphragm 182 whichis supported atop an upper cylindrical segment 184, which in turn islocated atop a lower cylindrical segment 186 extending above the surfaceof the valve diaphragm 170. The upper cylindrical segment 184 and thelower cylindrical segment 186 have identical inner diameters, with alower cylindrical segment 186 having a greater outer diameter than theupper cylindrical segment 184. A portion of the top of the lowercylindrical segment 186 extends outwardly around the bottom of the uppercylindrical segment 184, creating a lip 188. In the preferredembodiment, the pressure diaphragm 182 may be domed slightly, as seen inFIG. 11.

Turning now to FIGS. 13 through 23, a retainer cap 190 is shown whichfits over the valve diaphragm 170 after it is mounted on the top of theupper surface 102 of the cassette body 100. The retainer cap 190 thusfunctions to cover the top of the cassette body 100, retaining the valvediaphragm 170 between the retainer cap 190 and the cassette body 100 ina sealing fashion. The retainer cap 190 thus has the same generaloutline when viewed from the top (FIG. 13) as the cassette body 100(FIG. 1). Located in the bottom of the retainer cap 190 (FIG. 14) aresix pins 192, 194, 196, 198, 200, and 199, which are to be received bythe hollow cylinders 154, 156, 158, 160, and 162 and the aperture 161,respectively, in the cassette body 100 to align the retainer cap 190 onthe cassette body 100. Also located in the bottom of the retainer cap190 is a tab 202 to be received by the slot 164, and a tab 204 to bereceived by the slot 166.

The retainer cap 190 has three apertures 206, 208, and 210 therethroughlocated to coincide with the locations of the first cassette identifyingindicia 148, the second cassette identifying indicia 150, and the thirdcassette identifying indicia 152, respectively. The size of the threeapertures 206, 208, and 210 is sufficient to receive the small, solidcylinders which the first cassette identifying indicia 148 and the thirdcassette identifying indicia 152 comprise.

Located in the retainer cap 190 is a rectangular aperture 212 (FIGS. 13,14, 19 and 20) for placement over the domed portion 178 on the valvediaphragm 170. The rectangular aperture 212 in the retainer cap 190 isslightly larger than the domed portion 178 on the valve diaphragm 170 toprevent any closure of the cavity 180 formed by the domed portion 178when the retainer cap 190 is placed over the valve diaphragm 170 and thecassette body 100. The domed portion 178 of the valve diaphragm 170therefore will protrude through the rectangular aperture 212 in theretainer cap 190. In the bottom of the retainer cap 190 around therectangular aperture 212 is a U-shaped groove 214 (FIG. 14) designed toaccommodate the U-shaped raised rib 181 on the valve diaphragm 170.

Also located in the retainer cap 190 is a circular aperture 216 (FIGS.13 and 14), which has a diameter slightly larger than the outer diameterof the upper cylindrical segment 184 on the valve diaphragm 170, toallow the upper cylindrical segment 184 and the pressure diaphragm 182to protrude from the circular aperture 216 in the retainer cap 190. Thediameter of the circular aperture 216 is smaller than the outer diameterof the lower cylindrical segment 186 on 170, and on the bottom of theretainer cap 190 is disposed concentrically around the circular aperture216 a cylindrical recess 218 to receive the lower cylindrical segment186 on the valve diaphragm 170. Disposed in the cylindrical recess 218on the bottom side of the retainer cap 190 is a circular raised bead 220(FIGS. 14, 19, and 21) to help in the sealing of the cassette as it isassembled.

The retainer cap 190 has a front edge 222 (FIG. 16), a back edge 224(FIG. 15), and left (FIG. 18) and right (FIG. 17) side edges 226 and228, respectively. The edges 222, 224, 226, and 228 will contact the topof the upper surface 102 of the cassette body 100 when the retainer cap190 is assembled onto the cassette body 100 with the valve diaphragm 170disposed therebetween. The retainer cap 190 is attached to the cassettebody 100 in the preferred embodiment by ultrasonic welding, butadhesives or other bonding techniques known in the art may also be used.

Referring next to FIGS. 22 through 26, a bubble chamber cap 230 isillustrated which is for placement onto the open bottom of the bubbletrap 104 (FIG. 4). The bubble chamber cap 230 is on the bottom (FIG. 23)the same size as the outer edges of the bottom of the bubble trap 104(FIG. 4), and has a tab 232 (FIGS. 22 through 24) on the bottom whichwill project toward the back of the cassette beyond the back edge of thebubble trap 104. The bubble chamber cap 230 has a rectangular wallportion 234 (FIG. 24) extending upward from the bottom of the bubblechamber cap 230 and defining therein a square space, which rectangularwall portion 234 is sized to fit inside the bubble chamber 106 (FIG. 4).

Located at the front and left sides of the rectangular wall portion 234and extending upwards from the bottom of the bubble chamber cap 230 isan inlet cylinder 236 (FIGS. 22, 24, and 26) having an inlet aperture238 extending therethrough. The inlet aperture 238 extends through thebottom of the bubble chamber cap 230 (FIGS. 23 and 25), and is designedto receive from the bottom of the bubble chamber cap 230 a length oftubing therein. The bubble chamber cap 230 is attached to the bottom ofthe bubble trap 104 in the cassette body 100 in the preferred embodimentby ultrasonic welding, but adhesives or other bonding techniques knownin the art may also be used.

When the bubble chamber cap 230 is mounted to the bubble trap 104, theinlet cylinder 236 extends up to at least half of the height of thebubble chamber 106 (FIG. 7), and the siphon tube 108 (FIG. 7) drawsfluid from the bottom of the siphon tube 108 in the space within therectangular wall portion 234 of the bubble chamber cap 230 (FIG. 26). Itwill be appreciated by those skilled in the art that fluid will enterthe bubble chamber 106 through the inlet aperture 238 in the inletcylinder 236 near the top of the siphon tube 108, maintaining all airbubbles above the level near the bottom of the bubble chamber 106 atwhich fluid is drawn from the bubble chamber 106 by the siphon tube 108.

Moving now to FIGS. 27 through 32, a slide latch 240 is disclosed whichserved two main functions in the cassette. The slide latch 240 firstserves to latch the cassette into place in a main pump unit. It alsoserves to block the flow of fluid through the cassette when it is notinstalled, with the closing of the slide latch 240 to lock the cassetteinto place on the main pump unit also simultaneously allowing the flowof fluid through the cassette. The slide latch 240 slides from the frontof the cassette body 100 (FIG. 2) between the latch supporting finger124 and the latch supporting finger 126.

The slide latch 240 has an essentially rectangular, flat front portion242 (FIG. 31) which is of a height equal to the height of the cassettebody 100 with the retainer cap 190 and the bubble chamber cap 230installed, and a width equal to the distance between the left side ofthe bubble trap 104 and the left side of the cassette body 100. Twosmall notches 244 and 246 are removed from the back side of the frontportion 242 at the top thereof (FIGS. 27, 28, and 30), the small notch244 being removed at a location near the left corner, and the smallnotch 246 being removed at the right corner.

Extending from the back side of the front portion 242 aboutthree-quarters of the way down towards the back is a horizontal bottomportion 248 (FIG. 29), which has its edges directly below the closestedges of the small notch 244 and the small notch 246. Extending from theinner edge of the small notch 244 at the top of the slide latch 240 downto the bottom portion 248 is an inverted angled or L-shaped portion 250.Similarly, extending from the inner edge of the small notch 246 at thetop of the slide latch 240 down to the bottom portion 248 is aninverted, backwards angled or L-shaped portion 252 (FIGS. 27 and 28).

Spaced outwardly from the left side of the bottom portion 248 and theleft side of the leg of the inverted L-shaped portion 250 is a leftslide side 254. Likewise, spaced outwardly from the right side of thebottom portion 248 and the right side of the leg of the inverted,backwards L-shaped portion 252 is a right slide side 256 (FIGS. 28 and30). The left and right slide sides 254 and 256 are located slightlyabove the bottom of the bottom portion 248 (FIG. 30). The left and rightslide sides 254 and 256 are of a height to be engaged in the latchsupporting finger 124 and the latch supporting finger 126 (FIG. 2),respectively.

Located in the bottom portion 248 is an elongated, tear-shaped aperture258 (FIG. 29), with the wider portion thereof toward the front of theslide latch 240 and the extended narrower portion thereof toward theback of the slide latch 240. When the slide latch 240 is inserted intothe latch supporting finger 12 and the latch supporting finger 126 onthe cassette body 100, and the slide latch 240 is pushed fully towardthe back of the cassette body 100, the wider portion of the elongated,tear-shaped aperture 258 will be aligned with the aperture 142 in theoutlet tube mounting cylinder 144 (FIG. 4) to allow a segment of tubing(not shown) leading from the aperture 142 to be open. When the slidelatch 240 is pulled out from the front of the cassette body 100, thesegment of tubing (not shown) will be pinched off by the narrowerportion of the elongated, tear-shaped aperture 258.

It is critical that the design and location of the elongated,tear-shaped aperture 258 in the slide latch 240 ensure that the slidelatch 240 engages the main pump unit before the tubing is opened up, andfluid is allowed to flow through the cassette. Likewise, the tubing mustbe pinched off and the fluid path through the cassette must be blockedbefore the slide latch 240 releases the cassette from the main pumpunit. In addition, the choice of material for the slide latch 240 isimportant, with a lubricated material allowing the pinching operation tooccur without damaging the tubing (not shown). Examples of suchmaterials are silicone or Teflon impregnated acetals such as Delren.

Located at the back of the slide latch 240 on the inside of the rightslide side 256 at the bottom thereof is a tab 257 (FIGS. 27, 30, and 32)which is used to engage the main pump unit with the cassette when theslide is closed. Located on the top side of the bottom portion 248 tothe right of the elongated, tear-shaped aperture 258 is a smallwedge-shaped retaining tab 259 (FIG. 27, 30, and 32). The retaining tab259 cooperates with the bottom of the slightly raised border 146 of thecassette body 100 (FIG. 2), to resist the slide latch 240 from beingfreely removed once installed into the cassette body 100. When the slidelatch 240 is pulled back out from the front of the cassette body 100 sothat the wider portion of the elongated, tear-shaped aperture 258 isaligned with the aperture 142 in the outlet tube mounting cylinder 144,the retaining tab 259 will engage the slightly raised border 146 (FIGS.2 and 4), resisting the slide latch 240 from being drawn further out.

Referring now to FIGS. 33 through 36, a one-piece piston cap and bootseal 260 is illustrated, which is the subject of the above-identifiedpatent application entitled "Piston Cap and Boot Seal for a MedicationInfusion System," and which is for use on and in the pump cylinder 112(FIGS. 3 and 8). The piston cap and boot seal 260 is of one-piececonstruction, and is made of flexible, resilient material, such assilastic (silicone rubber) or medical grade natural rubber. Naturalrubber may be used to minimize friction, since some sticking of asilicone rubber piston cap and boot seal 260 in the pump cylinder 112(FIG. 8) may occur. Teflon impregnated silastic or other proprietaryformulas widely available will overcome this problem. In addition, thepiston cap and boot seal 260 may be lubricated with silicone oil priorto installation in the pump cylinder 112. The advantage of usingsilastic is that it may be radiation sterilized, whereas natural rubbermust be sterilized using gas such as ethylene oxide. In addition,silastic has better wear characteristics than natural rubber, making itthe preferred choice.

The piston cap and boot seal 260 includes a piston cap portion indicatedgenerally at 262, and a boot seal portion comprising a retaining skirt264 and a thin rolling seal 266. The piston cap portion 262 includes ahollow cylindrical segment 268 having an enlarged, rounded piston caphead 270 located at the top thereof. The piston cap head 270 has aroughly elliptical cross-section, with an outer diameter on the sidessufficient to provide a dynamic seal in the main diameter bore 114 ofthe pump cylinder 112 (FIG. 8). The roughly elliptical configuration ofthe piston cap head 270 closely fits the top of the main diameter bore114 of the pump cylinder 112. Extending from the top of the piston caphead 270 at the center thereof is a frustroconical segment 272, with thelarger diameter of the frustroconical segment 272 being at the bottomthereof attached to the piston cap head 270. The frustroconical segment272 is of a size to closely fit in the smaller diameter aperture 118 ofthe pump cylinder 112 (FIG. 8).

The hollow cylindrical segment 268 and the piston cap head 270 togetherdefine a closed end of the piston cap and boot seal 260 to receive apiston, which will be described below. The hollow cylindrical segment268 has located therein a smaller diameter portion 274, which smallerdiameter portion 274 is spaced away from the bottom of the piston caphead 270 to provide retaining means to retain a piston in the hollowcylindrical segment 268 between the piston cap head 270 and the smallerdiameter portion 274.

The retaining skirt 264 is essentially cylindrical, and is designed tofit snugly around the outer diameter of the pump cylinder 112 (FIG. 8).Prior to installation and with the piston cap and boot seal 260 in arelaxed configuration as shown in FIGS. 33 through 36, the retainingskirt 264 is located roughly around the hollow cylindrical segment 268.The retaining skirt 264 has an internal diameter sufficiently small toretain the retaining skirt 264 in position around the pump cylinder 112(FIG. 8) without moving when the piston cap portion 262 moves.

Located around the inner diameter of the retaining skirt 264 is atortuous path 276 leading from one end of the retaining skirt 264 to theother. The tortuous path 276 is required for sterilization of theassembled cassette, to allow the sterilizing gas to sterilize the areabetween the inside of the pump cylinder 112 and the piston cap and bootseal 260, which would be closed and may remain unsterilized if thetortuous path 276 did not exist. In addition, since the sterilizing gasis hot and cooling occurs rapidly after the sterilizing operation, thetortuous path 276 allows pressure equalization to occur rapidly where itotherwise would not. In the preferred embodiment, the tortuous path 276is a series of threads in the inner diameter of the retaining skirt 264.

Completing the construction of the piston cap and boot seal 260 is therolling seal 266, which is a segment defined by rotating around thecenterline of the piston cap and boot seal 260 a U having a first leg atthe radius of the hollow cylindrical segment 268 and a second leg at theradius of the retaining skirt 264, with the top of the first leg of theU being attached to the bottom of the hollow cylindrical segment 268 andthe top of the second leg of the U being attached to the bottom of theretaining skirt 264. When the piston cap and boot seal 260 is installedand the piston cap portion 262 moves in and out in the main diameterbore 114 in the pump cylinder 112 (FIG. 8), the legs of the U will varyin length, with one leg becoming shorter as the other leg becomeslonger. In this manner, the rolling seal 266 provides exactly what itsname implies-- a seal between the piston cap portion 262 and theretaining skirt 264 which rolls as the piston cap portion 262 moves.

Referring now to FIGS. 37 through 42, a piston assembly 280 is shownwhich drives the piston cap portion 262 of the piston cap and boot seal260 (FIG. 36) in the pump cylinder 112 (FIG. 8). The piston assembly 280has a rectangular base 282 which is positioned horizontally and locateddirectly behind the bubble chamber cap 230 (FIG. 24) when the piston capportion 262 is fully inserted into the pump cylinder 112. Therectangular base 282 has a notch 284 (FIGS. 41 and 42) in the front edgethereof, which notch is slightly larger than the tab 232 in the bubblechamber cap 230 (FIG. 23).

Extending upward from the front edge of the rectangular base 282 on theleft side of the notch 284 is an arm 286, and extending upward from thefront edge of the rectangular base 282 on the right side of the notch284 is an arm 288. At the top of the arms 286 and 288 is a verticallyextending rectangular portion 290 (FIG. 38). The rectangular portion 290as well as the upper portions of the arms 286 and 288 are for insertioninto and between the piston retaining finger 120 and the pistonretaining finger 122 in the cassette body 100 (FIG. 4).

The top of the rectangular portion 290 will contact the bottom of theupper surface 102 of the cassette body 100 (FIG. 8) to limit the upwardmovement of the piston assembly 280, the rectangular base 282 beingapproximately even with the bubble chamber cap 230 (FIG. 24) installedin the bottom of the bubble trap 104 of the cassette body 100 when thepiston assembly 280 is in its fully upward position. The bottom of therectangular portion 290 (FIG. 42) will contact the tab 232 on the bubblechamber cap 230 (FIG. 24) when the piston assembly 280, the piston head296, and the piston cap portion 262 (FIG. 36) are fully retracted fromthe pump cylinder 112 (FIG. 8).

Extending upwards from the top of the rectangular base 282 near the backedge of the rectangular base 282 and located centrally with respect tothe side edges of the rectangular base 282 is a cylindrical piston rod292. At the top of the piston rod 292 is a reduced diameter cylindricalportion 294, and mounted on top of the reduced diameter cylindricalportion 294 is a cylindrical piston head 296. The diameter of the pistonhead 296 is larger than the diameter of the reduced diameter cylindricalportion 294, and the top of the piston head 296 has rounded edges in thepreferred embodiment. The piston head 296 is designed to be received inthe portion of the hollow cylindrical segment 268 between the smallerdiameter portion 274 and the piston cap head 270 in the piston capportion 262 (FIG. 36). The reduced diameter cylindrical portion 294 islikewise designed to be received in the smaller diameter portion 274 ofthe piston cap portion 262.

The top of the piston head 296 is slightly above the top of therectangular portion 290, and when the piston assembly 280 is in itsfully upward position, the piston head 296 will have brought the pistoncap head 270 and the frustroconical segment 272 thereon (FIG. 36) to thetop of the pump cylinder 112 and into the smaller diameter aperture 118(FIG. 8), respectively, to completely eliminate volume both within thepump cylinder 112 and within the smaller diameter aperture 118.

Completing the construction of the piston assembly 280 are two raisedbeads 298 and 300, with the raised bead 298 being on the top surface ofthe rectangular base 282 on the left side of the piston rod 292, and theraised bead 300 being on the top surface of the rectangular base 282 onthe right side of the piston rod 292. Both of the raised beads 298 and300 extend from the sides of the piston rod 292 laterally to the sidesof the rectangular base 282. The raised beads 298 and 300 will be usedto center the piston assembly 280 with the jaws of the main pump unitused to drive the piston assembly 280, as well as to facilitateretaining the piston assembly 280 in the jaws.

Referring next to FIGS. 43 and 44, a tubing adapter 301 is illustratedwhich is located between an outlet tubing 306 extending from anassembled cassette 302 and a delivery tubing 303 which leads to thepatient. The tubing adapter 301 is essentially cylindrical, and ishollow throughout allowing the inlet tubing 306 and the delivery tubing303 to be inserted thereinto. The inlet tubing 306 and the deliverytubing 303 are in the preferred embodiment adhesively secured in thetubing adapter 301. Located at the top end of the tubing adapter 301 isa tapered portion 305, with the taper being on the outside of the tubingadapter 301 and having a smaller outer diameter as it approaches the topend of the tubing adapter 301. Located below the tapered portion 305 isa radially outwardly extending flange 307.

The assembly and configuration of the cassette may now be discussed,with reference to an assembled cassette 302 in FIGS. 45 through 48, aswell as to other figures specifically mentioned in the discussion. Thevalve diaphragm 170 is placed over the top of the upper surface 102 ofthe cassette body 100, with the apertures 172, 174, and 176 placed overthe hollow cylinders 156, 160, and 162, respectively. The retainer cap190 is then located over the valve diaphragm 170 and the cassette body100, and is secured in place by ultrasonic welding. Note again thatwhile adhesive sealing may be used, it is more difficult to ensure theconsistent hermetic seal required in the construction of the cassette302.

The step of firmly mounting the retainer cap 190 onto the cassette body100 exerts a bias on the valve diaphragm 170 (FIG. 9) causing it to becompressed in certain areas, particularly over the slightly raisedborder 146 on the top surface of the upper surface 102 of the cassettebody 100 (FIG. 1). This results in excellent sealing characteristics,and encloses the various passageways located in the upper surface 102 ofthe cassette body 100. The first passageway 128 is enclosed by the valvediaphragm 170, communicating at one end thereof with the aperture 110and at the other end thereof with the area between the cavity 180 andthe upper surface 102 of the cassette body 100. The second passageway134 also communicates with the area between the cavity 180 and the uppersurface 102 of the cassette body 100 at one end thereof, with the otherend of the second passageway 134 communicating with one end of thepassageway 132 in the pressure plateau 130.

The pressure diaphragm 182 is located above the surface of the pressureplateau 130, and a space exists between the edges at the side of thepressure plateau 130 and the inner diameters of the upper cylindricalsegment 184 and the lower cylindrical segment 186. This allows thepressure diaphragm 182 to be quite flexible, a design feature essentialto proper operation of the pressure monitoring apparatus. It maytherefore be appreciated that the flow area between the secondpassageway 134 and the third passageway 136 is not just the area of thepassageway 132, but also the area between the pressure diaphragm 182 andthe pressure plateau 130, as well as the area around the sides of thepressure plateau 130 adjacent the upper cylindrical segment 184 and thelower cylindrical segment 186.

The third passageway 136 (FIG. 1) is also enclosed by the valvediaphragm 170 (FIG. 9), and communicates at one end with the other endof the passageway 132, and at the other end with the recessed lensportion 138. The fourth passageway 140 is enclosed by the valvediaphragm 170, and communicates at one end with the recessed lensportion 138 and at the other end with the aperture 142.

Next, the bubble chamber cap 230 is placed on the bottom of the bubblechamber 106, and is secured by ultrasonically sealing the bubble chamberca 230 to the cassette body 100. The piston cap portion 262 of thepiston cap and boot seal 260 (FIG. 36) is inserted into the maindiameter bore 114 of the pump cylinder 112 (FIG. 8), and pushed towardthe top of the main diameter bore 114. Simultaneously, the retainingskirt 264 is placed over the outside of the pump cylinder 112 and ismoved up the outer surface of the pump cylinder 112 to the positionshown in FIGS. 46 and 48, which is nearly to the top of the outersurface of the pump cylinder 112. Next, the piston head 296 of thepiston assembly 280 (FIGS. 37 and 40) is inserted into the hollowcylindrical segment 268 of the piston cap and boot seal 260, and isforced past the smaller diameter portion 274 until it snaps home,resting against the bottom of the piston cap head 270.

The slide latch 240 is then inserted into engagement with the cassettebody 100, which is accomplished by sliding the left slide side 254 intothe latch supporting finger 124 on the right side thereof and by slidingthe right slide side 256 into the latch supporting finger 126 on theleft side thereof. The slide latch 240 is then pushed fully forward toalign the wider portion of the elongated, tear-shaped aperture 258 withthe outlet tube mounting cylinder 144. An inlet tube 304 is adhesivelysecured in the inner diameter of the inlet aperture 238 in the bubblechamber cap 230, in fluid communication with the bubble chamber 106. Theoutlet tube 306 extends through the wider portion of the elongated,tear-shaped aperture 258 and is adhesively secured in the inner diameterof the outlet tube mounting cylinder 144 in the cassette body 100, influid communication with the fourth passageway 140 through the aperture142.

The tubing adapter 301 is connected to the other end of the outlet tube306, and the delivery tube 303 is also attached to the tubing adapter301. The inlet tube 304 and the delivery tube 303 are shown in thefigures only in part; on their respective ends not connected to theassembled cassette 302 they may have connector fittings such as standardluer connectors (not shown), which are well known in the art. The use ofadhesives to attach the inlet tube 304, the outlet tube 306, and thedelivery tube 303 to the assembled cassette 302 and to the tubingadapter 301 also utilizes technology well known in the art. For example,adhesives such as cyclohexanone, methylene dichloride, ortetrahydrofuron (THF) may be utilized.

The Main Pump Unit

The preferred embodiment of the main pump unit used with the presentinvention includes a number of components used to hold, latch, and drivethe cassette described above. Referring first to FIGS. 49 through 53, alatch head 310 is illustrated which is used to grasp the raised bead 298and the raised bead 300 of the piston assembly 280 (FIG. 37). Extendingfrom the front of the latch head 310 at the top thereof on the left sideis a left jaw 312, and extending from the front of the latch head 310 atthe top thereof on the right side is a right jaw 314. The left and rightjaws 312 and 314 have curved indentations on the bottom sides thereof toreceive the raised bead 298 and the raised bead 300 (FIG. 37),respectively. A space between the left jaw 312 and the right jaw 314allows them to fit around the piston rod 292 of the piston assembly 280.

A cylindrical aperture 316 is located in the top of the latch head 310,which cylindrical aperture 316 is designed to receive a shaft on whichthe latch head 310 is mounted. A threaded aperture 318 in the back sideof the latch head 310 communicates with the cylindrical aperture 316,and will have locking means installed therein to lock a shaft in thecylindrical aperture 316. An aperture 320 extends through the latch head310 from the left side to the right side thereof near the back andbottom of the latch head 310.

A notch 322 is located in the latch head 310 at the bottom and frontthereof and in the center thereof, leaving a side portion 324 on theleft side and a side portion 326 on the right side. An aperture 328 islocated through the side portion 324, and an aperture 330 is locatedthrough the side portion 326, which apertures 328 and 330 are aligned.In addition, the portion of the latch head 310 including the left jaw312 has a raised edge 327 facing upward and backward, and a raised edge329 facing down and forward. The portion of the latch head 310 includingthe right jaw 314 has a raised edge 331 facing downward and forward. Theraised edges 327, 329, and 331 will be used to limit the movement of thelatch jaw, which will be discussed below.

A spring seat 332 is shown in FIGS. 54 and 55, which is designed to fitin the notch 322 in the latch head 310 (FIGS. 51 and 53). The springseat 332 has an aperture 334 extending therethrough from the left sideto the right side, which aperture 334 is slightly larger than theapertures 328 and 330 in the latch head 310. The spring seat 332 alsohas a cylindrical segment 336 extending from the front side thereof.

A latch jaw 340 is illustrated in FIGS. 56 through 58, which latch jaw340 is used to grasp the bottom of the rectangular base 282 of thepiston assembly 280 (FIG. 37) and maintain the left and right jaws 312and 314 of the latch head 310 (FIG. 51) in contact with the raised bead298 and the raised bead 300, respectively. The latch jaw 340 has a frontjaw portion 342 approximately as wide as the left and right jaws 312 and314 of the latch head 310, which jaw portion 342 is the portion of thelatch jaw 340 which contacts the bottom of the rectangular base 282 ofthe piston assembly 280. Extending back from the left side of the jawportion 342 is a left arm 344, and extending back from the right side ofthe jaw portion 342 is a right arm 346.

The left arm 344 has an aperture 348 (not shown) therethrough from theleft side to the right side at the end of the left arm 344 away from thejaw portion 342. Likewise, the right arm 346 has an aperture 350therethrough from the left side to the right side at the end of theright arm 346 away from the jaw portion 342. The apertures 348 and 350are slightly smaller in diameter than the aperture 320 in the latch head310 (FIGS. 49 and 50).

Extending upward from and at an approximately sixty degree angle withrespect to the right arm 346 from the end of the right arm 346 away fromthe jaw portion 342 is a driving arm 352. At the end of the driving arm352 which is not attached to the right arm 346 is a link pin 354extending to the right. Completing the construction of the latch jaw 340is a cylindrical recess 356 located in the back side of the jaw portion342, which cylindrical recess 356 has an inner diameter larger than theouter diameter of the cylindrical segment 336 of the spring seat 332(FIG. 55).

Referring now to FIGS. 59 through 61, the construction of a jawsassembly 360 from the latch head 310, the spring seat 332, and the latchjaw 340 is illustrated. The spring seat 332 fits within the notch 322and between the left jaw 312 and the right jaw 314 of the latch head310. A pin 362 is inserted through the aperture 328 in the side portion324, the aperture 334 in the spring seat 332, and the aperture 330 inthe side portion 326. The pin 362 is sized to fit snugly in theapertures 328 and 330, thereby retaining the pin 362 in place andallowing the spring seat 332 to rotate about the pin 362.

The latch jaw 340 is mounted onto the latch head 310 with the left jaw312 and the right jaw 314 of the latch head 310 facing the jaw portion342 of the latch jaw 340 using a pin 364. The pin 364 is insertedthrough the aperture 348 (not shown) in the left arm 344, the aperture320 in the latch head 310, and the aperture 350 in the right arm 346.The pin 364 is sized to fit snugly in the apertures 348 and 350, therebyretaining the pin 364 in place and allowing the latch jaw 340 to rotateabout the pin 364.

A spring 366 has one end thereof mounted over the cylindrical segment336 on the spring seat 332, and the other end thereof mounted in thecylindrical recess 356 in the latch jaw 340. The spring 366 acts to biasthe latch jaw 340 in either the open position shown in FIG. 59 with thejaw portion 342 of 340 away from the left jaw 312 and the left jaw 312of the latch head 310, or in the closed position shown in FIG. 61, withthe jaw portion 342 of the latch jaw 340 urged closely adjacent the leftjaw 312 and the right jaw 314 of the latch head 310. The movement of thelatch jaw 340 in both directions with respect to the latch head 310 islimited, to the position shown in FIG. 59 by the driving arm 352contacting the raised edge 327, and to the position shown in FIG. 61 bythe right arm 346 contacting the raised edge 329 and by the left arm 344contacting the raised edge 331. When the assembled cassette 302 isinstalled, movement of the latch jaw 340 to the position of FIG. 61 willalso be limited by the presence of the piston assembly 280, with therectangular base 282 being grasped by the jaws assembly 360. It will benoted that by moving the pin 354 either toward the front or toward theback, the latch jaw 340 may either be opened or closed, respectively.

Referring next to FIGS. 62 through 65, a main pump unit chassis 370 isillustrated which is designed to mount three independent pump unitsincluding three drive mechanisms into which three disposable assembledcassettes 302 may be installed. The assembled cassettes 302 are mountedon the bottom side of the pump chassis 370 shown in FIG. 62, with themotors and drive train being mounted on top of the pump chassis 370(FIG. 64) and being installed in a housing (not shown) mounted on top ofthe pump chassis 370.

Located on the pump chassis 370 are three pairs of angled segments 372and 374, 376 and 378, and 380 and 382. Each pair of angled segments 372and 374, 376 and 378, and 380 and 382 defines two facing channelstherebetween. In the preferred embodiment, the angled segments 372 and374, 376 and 378, and 380 and 382 are angled slightly further from thebottom of the pump chassis 370 near the front, to thereby have a cammingeffect as the assembled cassette 302 is installed and the slide latch240 is closed. Specifically, the angled segment 372 defines a channelfacing the angled segment 374, and the angled segment 374 defines achannel facing the angled segment 372. The angled segment 376 defines achannel facing the angled segment 378, and the angled segment 378defines a channel facing the angled segment 376. Finally, the angledsegment 380 defines a channel facing the angled segment 382, and theangled segment 382 defines a channel facing the angled segment 380.

Each of the pairs of angled segments 372 and 374, 376 and 378, and 380and 382 provides means on the bottom of pump chassis 370 for oneassembled cassette 302 to be securely latched to. The inverted L-shapedportion 250 and the inverted, backwards L-shaped portion 252 in theslide latch 240 (FIGS. 29 and 30) of the assembled cassette 302 aredesigned to facilitate attachment to one of the pairs of angled segments372 and 374, 376 and 378, and 380 and 382. With the slide latch 240pulled back away from the front of the assembled cassette 302, an areabetween the front portion 242 of the slide latch 240 and the top frontof the cassette body 100 and the retainer cap 190 is open, allowing thetop of the assembled cassette 302 to be placed over one of the pairs ofangled segments 372 and 374, 376 and 378, and 380 and 382.

By way of example, assume that the assembled cassette 302 is to bemounted in the first position (the position on the left end of the pumpchassis 370) on the first pair of angled segments 372 and 374. The topsurface of the assembled cassette 302, which is the retainer cap 190(FIG. 43), will mount against the bottom of the pump chassis 370 (FIG.62). In order to place the assembled cassette 302 in condition to beinstalled, the slide latch 240 is pulled back fully from the front ofthe assembled cassette 302, leaving an area between the front portion242 of the slide latch 240 and the front top portion of the assembledcassette 302 (made up of the cassette body 100 and the retainer cap 190)facing the front portion 242 of the slide latch 240.

The top of the assembled cassette 302 is then placed against the bottomof the pump chassis 370 with the first pair of angled segments 372 and374 fitting in the area between the front portion 242 of the slide latch240 and the front top portion of the assembled cassette 302. The slidelatch 240 is then pushed forward into the cassette body 100, sliding theinverted L-shaped portion 250 of the slide latch 240 into engagementwith the angled segment 372, and sliding the inverted, backwardsL-shaped portion 252 of the slide latch 240 into engagement with theangled segment 374. The assembled cassette 302 will thus be held inposition on the bottom of the pump chassis 370 until the slide latch 240is again pulled back, releasing the assembled cassette 302.

Projecting from the bottom of the pump chassis 370 are a number ofsegments used to position and align the assembled cassettes 302 in thefirst (the position on the left end of the pump chassis 370), second(intermediate), and third (the position on the right end of the pumpchassis 370) positions on the pump chassis 370. Three left lateralsupport walls 384, 386, and 388 protrude from the bottom of the pumpchassis 370 at locations to support the upper left side portion of theassembled cassettes 302 near the back thereof in proper positions in thefirst, second, and third positions, respectively. Likewise, three rightlateral support walls 390, 392, and 394 protrude from the bottom of thepump chassis 370 at locations to support the rear-most extending upperportion of the assembled cassettes 302 on the right side thereof inproper positions in the first, second, and third positions,respectively.

Additional support and positioning for the installation of the assembledcassettes 302 into the first, second, and third positions are providedfor the upper right back corner of the assembled cassettes 302 by threeright corner support walls 396, 398, and 400, respectively. The threeright corner support walls 396, 398, and 400 are L-shaped when viewedfrom the bottom (FIG. 62), and support and position the back of theassembled cassettes 302 behind the pump cylinders 112 (FIG. 4) and aportion of the right side of the assembled cassettes 302 adjacent thepump cylinders 112. Note that the three right lateral support walls 390,392, and 394 and the three right corner support walls 396, 398, and 400together provide continuous support and positioning for the assembledcassettes 302 in the first, second, and third positions, respectively.

Located in the raised material forming the left lateral support wall 384near the back thereof is a threaded aperture 402. A single segment ofraised material forms the right lateral support wall 390, the rightcorner support wall 396, and the left lateral support wall 386; locatedin that segment of raised material near the back thereof is a threadedaperture 404 on the left side near the right lateral support wall 390,and a threaded aperture 406 on the right side near the left lateralsupport wall 386. Likewise, a single segment of raised material formsthe right lateral support wall 392, the right corner support wall 398,and the left lateral support wall 388; located in that segment of raisedmaterial near the back thereof is a threaded aperture 408 on the leftside near the right lateral support wall 392, and a threaded aperture410 on the right side near the left lateral support wall 388. Finally, asingle segment of raised material forms the right lateral support wall394 and the right corner support wall 400 near the back thereof is athreaded aperture 412 near the right lateral support wall 394.

Located in the segment of raised material forming the right lateralsupport wall 390, the right corner support wall 396, and the leftlateral support wall 386 near the corner where the right lateral supportwall 390 and the right corner support wall 396 meet is an aperture 414which extends through the pump chassis 370 from top to bottom. Locatedin the segment of raised material forming the right lateral support wall392, the right corner support wall 398, and the left lateral supportwall 388 near the corner where the right lateral support wall 392 andthe right corner support wall 398 meet is an aperture 416 which extendsthrough the pump chassis 370 from top to bottom. Located in the segmentof raised material forming the right lateral support wall 394 and theright corner support wall 400 near the corner where the right lateralsupport wall 394 and the right corner support wall 400 meet is anaperture 418 which extends through the pump chassis 370 from top tobottom.

Note that with the assembled cassettes 302 positioned and mounted in thefirst, second, and third positions, the aperture 414, the aperture 416,and the aperture 418, respectively, will be directly back of the pistonrods 292 of the assembled cassettes 302 (FIG. 46). The apertures 414,416, and 418 will be used to mount the drive shafts connected to thejaws assembles 360 (FIGS. 59 through 61) used to drive the pistonassembly 280.

Located between the left lateral support wall 384 and the right lateralsupport wall 390 is a longitudinal rectangular recess 420 in the bottomsurface of the pump chassis 370. Similarly, located between the leftlateral support wall 386 and the right lateral support wall 392 is alongitudinal rectangular recess 422 in the bottom surface of the pumpchassis 370. Finally, located between the left lateral support wall 384and the right lateral support wall 390 is a longitudinal rectangularrecess 424 in the bottom surface of the pump chassis 370. While therectangular recesses 420, 422, and 424 do not extend through the pumpchassis 370, oval aperture 426, 428, and 430 smaller than therectangular recesses 420, 422, and 424 are located in the rectangularrecesses 420, 422, and 424, respectively, and extend through to the topside of the pump chassis 370.

The rectangular recesses 420, 422, and 424 will be used to mount sensormodules therein, and the oval aperture 426, 428, and 430 are to allowthe wires from the sensor modules to extend through the pump chassis370. Note that with the assembled cassettes 302 positioned and mountedin the first, second, and third positions, the rear-most extending upperportions of the assembled cassettes 302 will be located over therectangular recesses 420, 422, and 424. Located behind the oval aperture426, 428, and 430 are rectangular apertures 427, 429, and 431,respectively. The rectangular apertures 427, 429, and 431 are to allowthe wires from the ultrasonic sensors to extend through the pump chassis370.

Located in front of the right corner support wall 396 is a circularrecess 432 in the bottom surface of the pump chassis 370. Similarly,located in front of the right corner support wall 398 is a circularrecess 434 in the bottom surface of the pump chassis 370. Finally,located in front of the right corner support wall 400 is a circularrecess 436 in the bottom surface of the pump chassis 370. While thecircular recesses 432, 434, and 436 do not extend through the pumpchassis 370, square apertures 438, 440, and 442 smaller than thecircular recesses 432, 434, and 436 are located in the circular recesses432, 434, and 436, respectively, and extend through to the top side ofthe pump chassis 370.

The circular recesses 432, 434, and 436 will be used to mount valveactuator guides therein, and the cylindrical aperture 450, 452, and 454are to allow valve actuators to extend through the pump chassis 370 andto orient the valve actuator guides. Note that with the assembledcassettes 302 positioned and mounted in the first, second, and thirdpositions, the circular recess 432, the circular recess 434, and thecircular recess 436, respectively, will correspond exactly with thelocations of the domed portions 178 of the valve diaphragms 170 in theassembled cassettes 302 (FIG. 43).

Located to the left of the circular recess 432 and in front of therectangular recess 420 is a circular recess 444 in the bottom surface ofthe pump chassis 370. Similarly, located to the left of the circularrecess 434 and in front of the rectangular recess 422 is a circularrecess 446 in the bottom surface of the pump chassis 370. Finally,located to the left of the circular recess 436 and in front of therectangular recess 424 is a circular recess 448 in the bottom surface ofthe pump chassis 370. While the circular recesses 444, 446, and 448 donot extend through the pump chassis 370, cylindrical apertures 450, 452,and 454 of a smaller diameter than the circular recesses 444, 446, and448 are located in the circular recesses 444, 446, and 448,respectively, and extend through to the top side of the pump chassis370.

The circular recesses 444, 446, and 448 will be used to mount pressuretransducers therein, and the cylindrical apertures 438, 440, and 442 areto allow wires from the pressure transducers to extend through the pumpchassis 370. Note that with the assembled cassettes 302 positioned andmounted in the first, second, and third positions, the circular recess444, the circular recess 446, and the circular recess 448, respectively,will correspond with the locations of the pressure diaphragms 182 of thevalve diaphragms 170 in the assembled cassettes 302 (FIG. 43).

Projecting from the surface on the top side of the pump chassis 370 area number of raised segments in which threaded apertures are located tosupport the drive assembly. A cylindrical raised segment 456 is locatedto the left of the cylindrical aperture 450 on the top side of the pumpchassis 370. A laterally extending oval raised segment 458 is locatedbetween the square aperture 438 and the cylindrical aperture 452 on thetop side of the pump chassis 370. A second laterally extending ovalraised segment 460 is located between the square aperture 440 and thecylindrical aperture 454 on the top side of the pump chassis 370. Acylindrical raised segment 462 is located to the right of the squareaperture 442 and is laterally aligned with the rear-most portions of theoval raised segments 458 and 460. Finally, a cylindrical raised segment464 is located to the right of the square aperture 442 and is laterallyaligned with the front-most portions of the oval raised segments 458 and460.

Located in the cylindrical raised segment 456 is a threaded aperture466. Located in the oval raised segment 458 is a threaded aperture 468near the rear-most portion of the oval raised segment 458, a threadedaperture 470 near the front-most portion of the oval raised segment 458,and a threaded aperture 472 centrally located in the oval raised segment458. Similarly, located in the oval raised segment 460 is a threadedaperture 474 near the rear-most portion of the oval raised segment 460,a threaded aperture 476 near the front-most portion of the oval raisedsegment 460, and a threaded aperture 478 centrally located in the ovalraised segment 460. Located in the cylindrical raised segment 462 is athreaded aperture 480. Finally, located in the cylindrical raisedsegment 464 is a threaded aperture 482.

The apertures 414, 416, and 418 through the pump chassis 370 terminatein raised segments extending from the top surface of the pump chassis370. A raised segment 484 is located around the opening of the aperture414 on top of the pump chassis 370, a raised segment 486 is locatedaround the opening of the aperture 416 on top of the pump chassis 370,and a raised segment 488 is located around the opening of the aperture418 on top of the pump chassis 370.

Extending upwardly from the raised segment 484 behind the aperture 414on the left side is a guide finger 490, and on the right side is a guidefinger 492. The guide fingers 490 and 492 are parallel and have a spacetherebetween. Extending upwardly from the raised segment 486 behind theaperture 416 on the left side is a guide finger 494, and on the rightside is a guide finger 496. The guide fingers 494 and 496 are paralleland have a space therebetween. Extending upwardly from the raisedsegment 488 behind the aperture 418 on the left side is a guide finger498, and on the right side is a guide finger 500. The guide fingers 498and 500 are parallel and have a space therebetween.

Referring now to FIGS. 66 through 69, a cassette guide 510 for use inguiding the installation of the assembled cassette 30 into the properlocation for latching on the pump chassis 370 is illustrated. Disposedto the rear of the cassette guide 510 at the right side is an aperture512, and at the left side is an aperture 514. The aperture 512 will bealigned With the threaded aperture 404 (FIG. 62), the threaded aperture408, or the threaded aperture 412 while the aperture 514 will be alignedwith the threaded aperture 402, the threaded aperture 406, or thethreaded aperture 410 to install the cassette guide 510 in either thefirst, second, or third position.

The top side (FIG. 66) of the cassette guide 510 has a rectangularrecess 516 therein, which rectangular recess 516 corresponds in size tothe rectangular recesses 420, 422, and 424 in the pump chassis 370. Theoptical sensor modules will be accommodated between the rectangularrecesses 516 in the cassette guides 510 and the rectangular recesses420, 422, and 424 in the pump chassis 370. The right side of thisrectangular recess 516 is exposed through a rectangular aperture 518 onthe bottom of the cassette guide 510 (FIG. 67).

An area 520 on the bottom of the cassette guide 510 immediately to thefront of the rectangular aperture 518 and an area 522 to the right andto the back of the rectangular aperture 518 is recessed upward from thesurface 524 of the cassette guide 510. At the front right corner of therectangular aperture 518 a square segment 528 extends downward to thelevel of the surface 524 of the cassette guide 510. Located immediatelyforward of the square segment 528 is a thin rectangular track 530extending from the right side of the cassette guide 510. The thinrectangular track 530 terminates at the front end thereof in a blockingsegment 532.

The front end of the cassette guide 510 has a rounded notch 534 therein,which rounded notch 534 is positioned when the cassette guide 5-0 isinstalled on the pump chassis 370 to receive the outlet tube mountingcylinder 144 on the cassette body 100 (FIG. 4). When the cassette guide510 is installed on the pump chassis 370, the rear-most portion of theassembled cassette 302 will fit between the cassette guide 510 and thebottom of the pump chassis 370. Accordingly, the cassette guide 510together with the various support walls on the bottom of the pumpchassis 370 aids in the installation of the assembled cassettes 302 inthe proper position for latching.

Extending downward from the surface 524 is a hollow lower segment 511having a projection 513 extending toward the front. When the assembledcassette 302 is installed, the horizontal bottom portion 248 of theslide latch 240 will be located between the surface 524 and theprojection 513. The lower segment 511 is hollow to receive theultrasonic sensor housing, as will become apparent below. A hollowchimney 515 is located at the back of the cassette guide 510, and is incommunication with the interior of the lower segment 511. When thecassette guide 510 is installed on the pump chassis 370, the interior ofthe hollow chimney 515 will be in communication with one of therectangular apertures 427, 429, or 431 in the pump chassis 370, to allowwires from the ultrasonic sensor to extend therethrough.

Referring next to FIG. 70, a pump shaft 540 is illustrated which isessentially cylindrical. Near the top end of the pump shaft 540 on thefront side thereof a cam follower wheel 542 is mounted for rotationabout a short axle 544 extending orthogonally from the pump shaft 540.On the front side of the pump shaft 540 at the same location analignment wheel 546 is mounted for rotation about a short axle 548extending orthogonally from the pump shaft 540 on the opposite side ofthe short axle 544. Near the bottom end of the pump shaft 540 on therear side thereof is a conical recess 550, which will be used to attachthe jaws assembly 360 (FIG. 59 through 61) to the pump shaft 540.

Referring next to FIGS. 71 through 76, a slide lock 560 which is formounting on the thin rectangular track 530 of the cassette guide 510(FIG. 67) is illustrated. The slide lock 560 has a U-shaped slidechannel 562 at the front thereof, with the open portion of the U facingleft and extending from front to rear. The right side of the slidechannel 562, which is the bottom of the U, has a rectangular notch 564located near the front thereof, which notch 564 runs from the top to thebottom of the slide channel 562.

Extending back from the rear of the slide channel 562 at the bottomthereof is a thin rectangular connecting segment 566, which effectivelyextends from the leg of the U at the bottom of the slide channels 562.Attached at the rear edge of the rectangular connecting segment 566 is aU-shaped channel 568 with the open portion of the U facing right andextending from top to bottom. The forward leg of the U of the U-shapedchannel 568 is attached to the rectangular connecting segment 566 at thetop of the U-shaped channel 568. It will be appreciated that the topsurface of the rectangular connecting segment 566 and the top of theU-shaped channel 568 (which is U-shaped) are coplanar, and that theinterior surface of the lowermost leg of the slide channel 562 is alsocoplanar.

The upper left edge of the U-shaped channel 568 has a bevel 570 locatedthereon, with the bevel 570 being best illustrated in FIG. 76. Thefunction of the bevel 570 is as a light reflector, and will becomeapparent later in conjunction with the discussion of the mechanism forlatching the assembled cassette 302.

The power module to drive the main pump unit is not described herein,since it is not in any way related to the subject matter of the presentinvention. For a complete description of the construction of the powermodule, the above incorporated by reference application U.S. Ser. No.128,121, entitled "Air-In-Line Detector for a Medication InfusionSystem," may be referred to.

Referring next to FIGS. 77 through 80, an upper ultrasonic housing 800is illustrated. The upper ultrasonic housing 800 is hollow, and is openon the bottom thereof. The upper surface of the upper ultrasonic housing800 has a U-shaped ridge 802 and a straight ridge 804 located thereon,with a rectangular aperture 806 located therebetween in the uppersurface of the upper ultrasonic housing 800. The U-shaped ridge 802 andthe straight ridge 804 are sized to fit within the lower segment 511 ofthe cassette guide 5-0 (FIG. 69).

Located in the front of the upper ultrasonic housing 800 is a slot 808for receiving therein the outlet tube 306 of the assembled cassette 302.The slot 808 is deeper than it is wide, and has a funnel-shaped entranceto allow the outlet tube 306 to easily be directed into the slot 808. Inthe preferred embodiment, the width of the slot 808 is narrower than theoutside diameter of the outlet tube 306, causing the outlet tube 306 tofit in the slot 808 in a manner deforming the outlet tube 306.

The interior of the upper ultrasonic housing 800 may be thought of asthree areas, one on each side of the slot 808, and a third area in theportion of the upper ultrasonic housing 800 in which the slot 808 doesnot extend. The first two areas are locations in which ultrasonictransducers (not shown) will be located, and the third area will be thelocation of a miniature printed circuit board (not shown). Referringparticularly to FIG. 80, the first area, in the front and on the rightside of the upper ultrasonic housing 800, is bounded by a wall 810 onthe right side of the slot 808. The second area, in the front and on theleft side of the upper ultrasonic housing 800, is bounded by a wall 812on the left side of the slot 808.

Referring now to FIGS. 81 through 83, a lower ultrasonic housing 814which will mount onto the bottom of the upper ultrasonic housing 800 isillustrated. Like the upper ultrasonic housing 800, the lower ultrasonichousing 814 is hollow, but the lower ultrasonic housing 814 is open onthe top side thereof. The front portion of the lower ultrasonic housing814 (the portion which will be under the first two areas inside theupper ultrasonic housing 800) is shallow, while the rear portion of thelower ultrasonic housing 814 is deeper. The lower ultrasonic housing 814also has a slot 816 located therein, which slot 816 will be locatedunder the slot 808 in the upper ultrasonic housing 800 when the lowerultrasonic housing 814 is mounted on the upper ultrasonic housing 800.The slot 816 also has a funnel-shaped entrance, like the slot 808.

Located under the portion of the lower ultrasonic housing 814 having theslot 816 therein is a recessed area 818. The recessed area 818 islocated on both the left side and the right side of the slot 816 in thelower ultrasonic housing 814. In the preferred embodiment, the recessedarea 818 is frustroconically shaped, as best shown in FIGS. 83 and 83A.The frustroconically shaped recessed area 818 is spaced slightly awayfrom the front of the lower ultrasonic housing 814. Located on thebottom and at the front of the lower ultrasonic housing 814 on each sideof the slot 816 therein are two ramps 820 and 822 which are inclinedtoward the frustroconically shaped recessed area 818.

The recessed area 818 and the two ramps 820 and 822 are designed tocapture and retain the tapered portion 305 of the tubing adapter 301(FIG. 43) therein. Accordingly, the size of the recessed area 818 isapproximately identical to the size of the tapered portion 305 of thetubing adapter 301. The two ramps 820 and 822 are located as shown inFIG. 83A to draw the tapered portion 305 of the tubing adapter 301 froma position on the two ramps 820 and 822 to a position in contact withthe recessed area 818. This operation of engagement of the taperedportion 305 of the tubing adapter 301 with the recessed area 818 will befurther discussed in detail below.

Referring next to FIG. 84, a portion of a two-piece flex circuit 824 and825 is illustrated. The flex circuit 824 may be thought of as a straightbase portion having four arms extending orthogonally from the side ofthe base portion. At the end of each of the four arms is an exposedcircular conductive pad 826, 828, 830, or 832. A series of fourterminals 834, 836, 838, and 840 are located on the flex circuit 824 onthe base portion near the center thereof. The conductive pad 826 iselectrically connected to the terminal 834 by a conductor 850, theconductive pad 828 is electrically connected to the terminal 836 by aconductor 852, the conductive pad 830 is electrically connected to theterminal 838 by a conductor 854, and the conductive pad 832 iselectrically connected to the terminal 840 by a conductor 856.

The flex circuit 825 is a long tail segment having four terminals 842,844, 846, and 848 on the end adjacent the flex circuit 824. The baseportion of the flex circuit 824 and the flex circuit 825 are to belocated close together, and thus form a T. Four more conductors 858,860, 862, and 864 are located in the flex circuit 825. The conductor 858is electrically connected to the terminal 842, the conductor 860 iselectrically connected to the terminal 844, the conductor 862 iselectrically connected to the terminal 846, and the conductor 864 iselectrically connected to the terminal 848. It will be appreciated bythose skilled in the art that the conductors 850, 852, 854, and 856 andthe conductors 858, 860, 862, and 864 are electrically insulated on bothsides thereof.

Referring next to FIG. 85, the assembly of two ultrasonic transducers866 and 868 to the flex circuit 824 is illustrated. The transducers 866and 868 are typically ceramic ultrasonic transducers. In a typicalassembly of ultrasonic transducers, soldering is used, with the resultof possible damage to the ceramic ultrasonic transducer. The presentinvention instead uses conductive adhesive transfer tape, which hasadhesive on both sides and is electrically conductive. Such conductivetransfer tape is commercially available from 3M under the productidentification number 9703. A disc-shaped segment of conductive transfertape 870 is placed between the conductive pad 826 and one side (calledthe back side) of the ultrasonic transducer 866. The disc-shaped segmentof conductive transfer tape 870 both secures the conductive pad 826 tothe one side of the ultrasonic transducer 866 and makes electricalcontact between the conductive pad 826 and the one side of theultrasonic transducer 866.

A disc-shaped segment of conductive transfer tape 872 is placed betweenthe conductive pad 828 and the other side (the front side) of theultrasonic transducer 866. A disc-shaped segment of conductive transfertape 874 is placed between the conductive pad 830 and one side (thefront side) of the ultrasonic transducer 868. A disc-shaped segment ofconductive transfer tape 876 is placed between the conductive pad 832and the other side (the back side) of the ultrasonic transducer 868.Thus, the ultrasonic transducers 866 and 868 are assembled andelectrically connected to the flex circuit 824.

The disc-shaped segments of conductive transfer tape 870, 872, 874, and876 are used in the preferred embodiment. Instead of using conductivetransfer tape, conductive epoxy could be used, although the conductivetransfer tape is preferred.

Referring next to FIG. 86, the ultrasonic transducers 866 and 868 areassembled into the upper ultrasonic housing 800. The portion of the flexcircuit 824 on the side of the conductive pad 828 opposite theultrasonic transducer 866 is adhesively bonded to the wall 812, thussecuring the ultrasonic transducer 866 to the wall 812, Similarly, theportion of the flex circuit 824 on the side of the conductive pad 830opposite the ultrasonic transducer 868 is adhesively bonded to the wall810, thus securing the ultrasonic transducer 868 to the wall 810. Theadhesive used is preferably an elastomeric adhesive which goes on in athin coat with no air pockets. One such adhesive is Black Max adhesive.A small block of foam 878 is used to bear against the ultrasonictransducer 866 and the associated portions of the flex circuit 824attached thereto. Similarly, a small block of foam 880 is used to bearagainst the ultrasonic transducer 868 and the associated portions of theflex circuit 824 attached thereto.

The flex circuit 825 is directed through the rectangular aperture 806 inthe flex circuit 824. The connectors 858, 860, 862, and 864 areelectrically connected to a connector 882. Referring now to FIG. 87, asmall printed circuit board 884 having various components thereon iselectrically connected to the terminals 834, 846, 838, and 840 (FIG. 84)on the flex circuit 824 and the terminals 842, 844, 846, and 848 on theflex circuit 825. The printed circuit board 884 then rests in the thirdarea in the upper ultrasonic housing 800, as shown.

In an alternate embodiment illustrated in FIG. 85A, an aperture is usedon the conductive pads and the disc-shaped segments of conductivetransfer tape located on the back sides of each of the ultrasonictransducers 866 and 868. The conductive pad 826 and the disc-shapedsegment of conductive transfer tape 870 each have apertures extendingtherethrough on the back side of the ultrasonic transducer 866.Similarly, the conductive pad 832 and the disc-shaped segment ofconductive transfer tape 876 each have apertures extending therethroughon the back side of the ultrasonic transducer 868. The apertures allowthe ultrasonic transducers 866 and 868 to flex more freely, and thestrength of the output signal is approximately doubled by using theapertures as described.

The apertures in the conductive pads 826 and 832 and in the disc-shapedsegments of conductive transfer tape 870 and 876 are centrally locatedtherein. The diameters of the ultrasonic transducers 866 and 868, aswell as the diameters of the conductive pads 826, 828, 830, and 832 areapproximately 0.21 inches. In the preferred embodiment, the diameters ofthe apertures in the conductive pads 826 and 832 and in the disc-shapedsegments of conductive transfer tape 870 and 876 are approximately 0.125inches. The size of the apertures is dictated on the one hand by thedesire to maintain a low resistance connection and on the other hand bythe desire to maximize the amount of flexion in the ultrasonictransducers 866 and 868.

Referring next to FIGS. 88 through 90, an optical sensor module 670 isillustrated. The optical sensor module 670 is essentially rectangular incross-section, with a wider rectangular flange 672 on top of therectangular portion, and an oval portion 674 above the rectangularflange 672. A flex cable 676 extends from the top of the oval portion674. Located around the circumference of the oval portion 674 is agroove 678, which will receive an elastomeric O-ring, which will retainthe oval portion 674 of the optical sensor modules 670 in the ovalapertures 426, 428, or 430. The rectangular flange 672 of the opticalsensor modules 670 will fit into the rectangular recesses 420, 422, or424, in the first, second, or third pump positions, respectively.

The rectangular portion of the optical sensor module 670 has located inthe front thereof and immediately under the rectangular flange 672 anotch indicated generally by 680, which notch 680 will receive therearmost portion of the assembled cassette 302. Further details of theoptical sensor module 670 are not necessary for the purposes of thepresent application. For a complete description of the construction ofthe optical sensor module 670, the above incorporated by referenceapplication U.S. Ser. No. 128,121, entitled "Air-In-Line Detector for aMedication Infusion System," may be referred to.

Referring next to FIGS. 91 through 93, a valve actuator 620 isillustrated. The valve actuator 620 includes a thin, essentiallyrectangular portion 622, and has a circular bearing 624 rotatablymounted near the top thereof. The circular outer diameter of the bearing624 extends slightly above the top of the rectangular portion 622. Therectangular portion 622 of the valve actuator 620 has chamfered edges onthe lower end thereof as indicated generally at 625, and has a smallnotch 626, 628 in both lateral sides of the rectangular portion 622 at alocation above the lower end thereof. The small notches 626 and 628 arefor receiving means for retaining the valve actuator 620 in positiononce it is installed; this will become evident below in conjunction withthe discussion of the assembly of the main pump unit.

Moving next to FIGS. 94 and 95, a valve actuator guide 630 isillustrated which is used to guide and retain in position pairs of thevalve actuators 620. The upper portion 632 of the valve actuator guide630 is square in cross-section, and lower portion 634 is circular incross-section. Extending vertically through both the square upperportion 632 and the circular lower portion 634 of the valve actuatorguide 630 are two apertures 636 and 638, which are rectangular incross-section. The apertures 636 and 638 ar sized to allow therectangular portion 622 of the valve actuator 620 to slide freelytherein in each of the apertures 636 and 638.

One of the valve actuator guides 630 will be installed into each of thepump positions in the pump chassis 370. In the first pump position, thesquare upper portion 632 of the valve actuator guide 630 will be locatedin the square aperture 438 on the pump chassis 370 and the circularlower portion 634 of the valve actuator guide 630 will be located in thecircular recess 432 on the pump chassis 370. In the second pumpposition, the square upper portion 632 will be located in the squareaperture 440 and the circular lower portion 634 will be located in thecircular recess 434. In the third pump position, the square upperportion 632 will be located in the square aperture 442 and the circularlower portion 634 will be located in the circular recess 436.

Referring next to FIGS. 96 through 98, a pressure transducer 660 isillustrated. One of the pressure transducers 660 will be installed inthe pump chassis 370 in each pump position, in the circular recesses444, 446, and 448. The pressure transducer 660 is essentiallycylindrical, with a groove 662 located around the circumference of thepressure transducer 660. The groove 662 is to receive an elastomericO-ring, which will both retain the pressure transducers 660 in thecircular recesses 444, 446, and 448, and provide a fluid seal. Locatedon top of the pressure transducer 660 is a square segment 664 in whichis located the actual transducer, which square segment 664 will bereceived in the cylindrical apertures 450, 452, and 454. Extendingupward from the square segment 664 are several leads 666.

Referring next to FIGS. 99 and 100, a valve actuator seal 650 is shownwhich is used both to provide a fluid seal and, more importantly, toretain the valve actuators 620 (FIGS. 85 through 87) in an upwardposition with their bearings 624 against the lower portion 593 of thepower module cam 580. The outer circumference of the valve actuatorseals 650 is of a size allowing them to be retained in a friction fit inthe circular recesses 432, 434, and 436 below the valve actuator guides630. A metal ring (not shown) may be molded into the outer diameter ofthe valve actuator seals 650 to better enable them to be better retainedin the circular recesses 432, 434, and 436.

Two apertures 652 and 654, which are rectangular in configuration, arelocated in the valve actuator seal 650 to receive the bottom portions ofthe rectangular portion 622 of the valve actuator 620. The lengths ofthe apertures 652 and 654 are shorter than the width of the rectangularportion 622 of the valve actuator 620, with the small notches 626 and628 in the rectangular portion 622 being used to capture to ends of oneof the apertures 652 and 654. It will be appreciated that the smallnotches 626 and 628 of the valve actuators 620 will engage the apertures652 and 654 in the valve actuator seal 650, thereby allowing the valveactuator seal 650 to exert a bias on the valve actuators 620. As will beseen below, the bias exerted by the valve actuator seal 650 on the valveactuators 620 is an upward one, urging the valve actuators 620 againstthe lower portion 593 of the power module cam 580.

In the previous discussions of the various parts of the main pump unit,the function and interrelationship between parts has been brieflydiscussed. Before moving on to the operation of the main pump unit andthe assembled cassette 302, a brief discussion of the assembly of themain pump unit is in order. This discussion specifically refers to FIGS.62 through 65 (the pump chassis 370) and to FIGS. 101-103, and also toother figures which are specifically mentioned in the discussion.Details of the drive assembly are omitted in this specification.

A hollow cylindrical pump shaft bearing 640 is installed in both the topand the bottom of each of the apertures 414, 416, and 418 in the pumpchassis 370. In the preferred embodiment, the pump shaft bearings 640fit in the apertures 414, 416, and 418 in an interference fit to retainthem in the apertures 414, 416, and 418 in the pump chassis 370. Thepump shaft bearing 640 are preferably made of a low friction materialsuch as Teflon to allow the pump shafts 540 to move freely therein.

Next, the valve actuator guides 630 are installed from the bottom of thepump chassis 370 into the circular recess 432 and the square aperture438 in the first pump position, into the circular recess 434 and thesquare aperture 440 in the second pump position, and into the circularrecess 436 and the square aperture 442 in the third pump position. Withthe valve actuator guides 630 installed in the pump chassis 370 thebottom surface of the valve actuator guides 630 leaves a portion of thecircular recesses 432, 434, and 436 open from the bottom side of thepump chassis 370. The valve actuator seals 650 (FIGS. 97 and 98) will beinstalled later in the circular recesses 432, 434, and 436 below thevalve actuator guides 630.

The next step in the assembly is to install the pressure and opticalsensor modules. The pressure transducers 660 (FIGS. 96 through 98) areinstalled from the bottom of the pump chassis 370 into the circularrecesses 444, 446, and 448. The pressure transducers 660 are essentiallycylindrical, and with O-rings in the grooves 662 fit snugly into thecircular recesses 444, 446, and 448 with their bottom surfaces flushwith the bottom surface of the pump chassis 370 around the circularrecesses 444, 446, and 448; the tops of the cylindrical portion of thepressure transducers 660 fit against the cylindrical apertures 450, 452,and 454 in the pump chassis 370. Not shown in the drawings is thepreferred embodiment's use of a thin membrane adhesively placed over thebottom of the pressure transducer 660 and the portions of the bottomsurface of the pump chassis 370 thereabout. This thin membrane protectsthe pressure transducer 660 from fluids which may inadvertently oraccidentally end up on the device.

The optical sensor assembles 570 (FIGS. 88 through 90) are installed inthe rectangular recesses 420, 422, and 416 of the pump chassis 370, withthe oval portions 674 of the optical sensor modules 670 fitting into theoval apertures 426, 428, and 430. The optical sensor modules 670 areretained in position by the pressure of O-rings in the grooves 678 inthe optical sensor modules 670, and by the cassette guides 510.

The next step in the assembly of the main pump unit mechanicalcomponents onto the pump chassis 370 is the installation of the cassetteguide 510 (FIGS. 66 through 69) and the slide lock 560 (FIGS. 71 through76). The slide lock 560 is installed onto the cassette guide 510 byplacing the portion of the slide lock 560 including the bottom of theslide channel 562 into the rectangular aperture 518 in the cassetteguide 510 from the top, with the rectangular connecting segment 566 ofthe slide lock 560 extending over the portion of the area 522 in theback of the cassette guide 510. This aligns the interior of the U-shapedslide channel 562 on the slide lock 560 with the back end of the thinrectangular track 530 on the cassette guide 510. The slide lock 560 isthen moved forward with respect to the cassette guide 510, with theinterior of the slide channel 562 fitting over the thin rectangulartrack 530 until the blocking segment of the cassette guide 510 iscontacted by the slide lock 560.

The upper ultrasonic housing 800 and its associated components as shownin FIG. 87 are then covered by attaching the lower ultrasonic housing814. In the preferred embodiment, one of three manufacturing techniquesmay be used to attach the upper ultrasonic housing 800 and the lowerultrasonic housing 814 together. They may be adhesively securedtogether, they may be ultrasonically welded together, or a pottingmaterial may be used to fill the interiors of both components to producea potted assembly. The upper ultrasonic housing 800 is then adhesivelyattached to the cassette guide 510, with the flex circuit 825 extendingthrough the chimney 515 of the cassette guide 510. The U-shaped ridge802 and the straight ridge 804 fit into the interior of the lowersegment 511 of the cassette guide 510, and the adhesive securelyattaches the upper ultrasonic housing 800 to the cassette guide 510.

The cassette guides 510 together with the slide locks 560 may then bemounted into the three pump positions on the pump chassis 370, whichalready contain the optical sensor module 670, using two screws (notshown). In the first pump position, the flex circuit 825 which extendsthrough the chimney 515 of the cassette guide 510 is fed through therectangular aperture 427 in the pump chassis 370. A screw is placedthrough the aperture 514 in the cassette guide 510 into the threadedaperture 402 in the pump chassis 370, and a second screw is placedthrough the aperture 512 in the cassette guide 510 into the threadedaperture 404 in the pump chassis 370.

In the second pump position, the flex circuit 825 which extends throughthe chimney 515 of the cassette guide 510 is fed through the rectangularaperture 429 in the pump chassis 370. A screw is placed through theaperture 514 in the cassette guide 510 into the threaded aperture 406 inthe pump chassis 370, and a second screw is placed through the aperture512 in the cassette guide 510 into the threaded aperture 408 in the pumpchassis 370. In the third pump position, the flex circuit 825 whichextends through the chimney 515 of the cassette guide 510 is fed throughthe rectangular aperture 431 in the pump chassis 370. A screw is placedthrough the aperture 514 in the cassette guide 510 into the threadedaperture 410 in the pump chassis 370, and a second screw is placedthrough the aperture 512 in the cassette guide 510 into the threadedaperture 412 in the pump chassis 370. By way of example, the cassetteguide 510 and the slide lock 560 are shown mounted in the first pumpposition in FIG. 101.

Next, the pump shafts 540 are installed in the pump shaft bearings 640,which have previously been installed in the apertures 414, 416, and 418.The end of the pump shafts 540 containing the conical recess 550 thereinare inserted through the pump shaft bearings 640 from the top, with thealignment wheel 546 being located between one of the three pairs ofguide fingers, namely the guide fingers 490 and 492 for the first pumpposition, the guide fingers 494 and 496 for the second pump position,and the guide fingers 494 and 496 for the third pump position. Forexample, the pump shaft 540 is shown installed in the first pumpposition in FIG. 101.

The valve actuators 620 are installed next, with one pair of the valveactuators 620 being installed in each pump position. The bottom ends ofthe valve actuators 620 having the chamfered edges 625 are insertedthrough the top sides of the valve actuator guides 630, with one pair ofthe valve actuators 620 being installed in each of the three valveactuator guides 630. The pair of valve actuators 620 are inserted intothe apertures 636 and 638 in the valve actuator guides 630 with thebearings 624 on each of the pair of the valve actuators 630 facing awayfrom each other.

It will be appreciated that the rectangular portions 622 of the valveactuators 620 will extend downward through the apertures 636 and 638 inthe valve actuator guides 630. As stated above, valve actuator seals 650are used in each of the three pump positions, and are mounted from thebottom of the pump chassis 370 into the circular recesses 432, 434, and436 below the valve actuator guides 630. The outer circumference of thevalve actuator seals 650 causes them to be retained in a friction fit inthe circular recesses 432, 434, and 436.

The lower ends of the rectangular portions 622 of each pair of the valveactuators 620 extend downward through the apertures 652 and 654 in thevalve actuator seal 650. The small notches 626 and 628 in one of thevalve actuators 620 in each pair is retained in the aperture 652 in thevalve actuator seal 650, and the other one of the valve actuators 620 ineach pair is retained in the aperture 654. As shown in FIGS. 113 and114, the valve actuator seals 650 will tend to urge the valve actuators620 in an upward direction. In the preferred embodiment, the bottoms ofthe valve actuators 620 having the chamfered edges 625 will protrudesomewhat from the bottom surface of the pump chassis 370 around thecircular recesses 432, 434, and 436 even when the valve actuators 620are in their open position. For example, in their closed position theymay protrude approximately thirty thousands of an inch, and in theiropen position they may protrude seventy thousands of an inch.

This upward biasing of the valve actuator 620 is essential both to allowthe assembled cassettes 302 to be freely inserted, and to maintain thevalve actuators 620 in an upward position with their bearings 624against the lower portion 593 of the power module cam 580. The valveactuator seals 650 accordingly function both to provide a fluid seal andto bias the valve actuators 620 in the upward position described.

The next step in the assembly of the main pump unit is to install powermodule assemblies (one of which is shown in FIG. 101) onto each of thethree pump positions on the pump chassis 370. For the details of thisprocedure, the above incorporated by reference application U.S. Ser. No.128,121, entitled "Air-In-Line Detector for a Medication InfusionSystem," may be referred to.

The final component to be installed is the jaws assembly 360 (FIGS. 59through 61), with one jaws assembly 360 being installed in each of thethree pump positions onto the bottom of the pump shafts 540, which areinstalled in the apertures 414, 416, and 418. The bottom end of the pumpshaft 540 having the conical recess 550 therein is inserted into thecylindrical aperture 316 in the latch head 310 of the jaws assembly 360.A retaining screw (not shown) is screwed into the threaded aperture 318in the latch head 310, and into the conical recess 550 of the pump shaft540 to retain the jaws assembly 360 in place on the bottom of the pumpchassis 370.

The location of the installed jaws assembly 360 is shown in FIG. 102,with the slide lock 560 and the latch jaw 340 in the open position. Thelink pin 354 on the latch jaw 340 is located in the U-shaped channel 568of the slide lock 560, and movement of the slide lock 560 willaccordingly cause the latch jaw 340 to move. When the slide lock 560 isfully forward, as shown in FIG. 102, the latch jaw 340 will be in theopen position, with the jaw portion 342 of the latch jaw 340 away fromthe right jaw 314 of the latch head 310. When the slide lock 560 ispushed toward the back of the pump chassis 370, as shown in FIG. 103,the latch jaw 340 will be in the closed position, with the jaw portion342 of the latch jaw 340 closely adjacent the right jaw 314 of the latchhead 310.

This completes the discussion of the assembly of the main pump unit withthree pump positions. It is now appropriate to discuss the installationof the assembled cassette 302 into the first pump position. Theinstallation of the assembled cassette 302 into the other two pumppositions is identical to the installation into the first pump position.

With the slide latch 240 pulled back fully away from the front of theassembled cassette 302 (FIGS. 45 and 46), the wider portion of theelongated, tear-shaped aperture 258 in the slide latch 240 will closethe outlet tube 306, preventing fluid from flowing through the assembledcassette 302. The inlet tube 304 is connected to a fluid source such asan IV bag (not shown), and the delivery tubing 303 is connected to afluid delivery device such as an injection set (not shown), the use ofwhich is well known in the art. The slide latch 240 is opened, togetherwith any other closures in the IV bag line, and fluid fills the lines,the assembled cassette 302, and the injection set. By tapping or shakingthe assembled cassette 302 any residual air bubbles will flow outthrough the line. The slide latch 240 is then pulled back and the outlettube 306 is closed, and the system is in a primed condition with theassembled cassette 302 ready to be installed onto the main pump unit.

When the slide latch 240 is pulled back, an opening is left between thefront portion 242 of the slide latch 240 and the front top portion ofthe assembled cassette 302 (made up of the cassette body 100 and theretainer cap 190) facing the front portion 242 of the slide latch 240.By way of the example used herein where the assembled cassette 302 is tobe mounted in the first position (the position on the left end of thepump chassis 370), the opening between the front portion 242 of theslide latch 240 and the front top portion of the assembled cassette 302will admit the first pair of angled segments 372 and 374 as theassembled cassette 302 is installed. The top surface of the assembledcassette 302, which is the retainer cap 190 (FIG. 43), will mountagainst the bottom of the pump chassis 370 (FIG. 62).

Prior to installing the assembled cassette 302 into the main pump unit,the slide lock 560 must be fully forward with the latch jaw 340 openedaway from the latch head 310, as mentioned previously and as shown inFIG. 102. In addition, the jaws assembly 360 should be in its fullyupward position.

Referring now to FIG. 104, the rear-most edge of the assembled cassette302 is tilted upward in front of the first pump position. Note also theangled position of the tubing adapter 301. The rear-most edge of the topof the assembled cassette 302 is then placed against the bottom of thepump chassis 370 between the pressure transducer 660 (mounted flush withthe bottom of the pump chassis 370) and the top side of the cassetteguide 510, as shown in FIG. 105. As the assembled cassette 302 is sopositioned, the outlet tube 306 will begin to move into thefunnel-shaped entrances to the slots 808 and 816 in the upper ultrasonichousing 800 and the lower ultrasonic housing 814, respectively.Simultaneously, the top of the tapered portion 305 of the tubing adapter301 will contact the ramp 820 and 822 on the lower ultrasonic housing814, as shown in FIG. 105. This engagement is key, since the ramps 820and 822 will urge the tapered portion 305 of the tubing adapter 301rearward toward the recessed area 818.

The rear-most portion of the top of the assembled cassette 302 is slidtoward the back of the pump chassis 370 into position between the leftlateral support wall 384 on the left side thereof and the right lateralsupport walls 390 o the right side thereof, with most of the rear-mostportion of the top of the assembled cassette 302 fitting into the notch680 in the optical sensor module 670. The upper right back corner of theassembled cassette 302 is supported and positioned in the back of theassembled cassette 302 behind the pump cylinder 112 (FIG. 4) and on theportion of the right side of the assembled cassette 302 adjacent thepump cylinder 112 by the right corner support wall 396.

As this movement of the assembled cassette 302 rearward into engagementwith the main pump unit is occurring, the outlet tube 306 will continueto be pulled into the slots 808 and 816 in the upper ultrasonic housing800 and the lower ultrasonic housing 814, respectively. The taperedportion 305 of the tubing adapter 301 will slide back into the recessedarea 818, as shown in FIG. 106. Thus, the installation of the assembledcassette 302 into the main pump unit will automatically engage theoutlet tube 306 in position between the ultrasonic transducers 866 and868. The outlet tube 305 is deformed slightly in the slots 808 and 816since the width of the slots 808 and 816 is less than the outer diameterof the outlet tube 306. This ensures good contact of the outlet tube 306with the walls 810 and 812 in the upper ultrasonic housing 800, and thusgood contact with the ultrasonic transducers 866 and 868.

When the assembled cassette 302 is pushed fully back in place, the frontof the assembled cassette 302 is tilted upward against the bottom of thepump chassis 370, stretching slightly the outlet tube 306. At thispoint, the first pair of angled segments 372 and 374 on the bottom ofthe pump chassis 370 fitting into the area between the front portion 242of the slide latch 240 and the front top portion of the assembledcassette 302. The slide latch 240 may then be pushed into the cassettebody 100 as shown in FIG. 106, sliding the inverted L-shaped portion 250of the slide latch 240 into engagement with the angled segment 372, andsliding the inverted, backwards L-shaped portion 252 of the slide latch240 into engagement with the angled segment 374. The assembled cassette302 will thus be held in position on the bottom of the pump chassis 370until the slide latch 240 is again pulled back, releasing the assembledcassette 302.

Simultaneously, the outlet tube 306 will be opened, but fluid will notflow through the outlet tube 306 since at least one of the valveactuators 620 will be in its fully downward position at any given time,thereby preventing free flow through the assembled cassette 302 wheneverthe assembled cassette 302 is installed on the main pump unit. It willalso be noted that in this initially installed position, the piston capportion 262 is located at the very top of the pump cylinder 112.

The pumping operation of the system described above is not fullydescribed herein. Rather, for a complete description of the pumpingoperation the above incorporated by reference application U.S. Ser. No.128,121, entitled "Air-In-Line Detector for a Medication InfusionSystem," may be referred to.

The air-in-line detector of the present invention uses the pair ofultrasonic transducers 866 and 868 (FIG. 86) to detect the presence ofair in the outlet tube 306 of the assembled cassette 302 (FIG. 106). Thebasic principle of operation is simple--fluids readily propagateultrasonic energy while air or foam is a poor conductor of ultrasonicenergy, several orders of magnitude less than fluids. Assume for thediscussion of operation of the system that the ultrasonic transducer 866is the transmitter and the ultrasonic transducer 868 is the receiver.When the ultrasonic transducer 866 is driven by an oscillating signal ata resonant frequency, it will vibrate at that frequency. As the drivingfrequency moves away from the resonant frequency, the vibration willdiminish to a very small value at some distance away from the resonantfrequency. Thus, the strength of the vibrations is at a maximum at theresonant frequency, and will diminish as the driving frequency moveseither higher or lower than the resonant frequency.

In order for the system to function at its optimum, the ultrasonictransducer 866 and the ultrasonic transducer 868 should haveapproximately the same resonant frequency. The vibrations from theultrasonic transducer 866 are directed through a segment of tubing tothe ultrasonic transducer 868, where they will cause an output from theultrasonic transducer 868 which is proportional to the strength of thevibrations received by the ultrasonic transducer 868. If there is a goodconduit of vibrations between the ultrasonic transducer 866 and theultrasonic transducer 868, the output from the ultrasonic transducer 868will closely resemble the resonant input signal used to drive theultrasonic transducer 866.

When ultrasonic vibrations are generated by the ultrasonic transducer866, they must pass through the outlet tube 306 to reach the ultrasonictransducer 868. If the outlet tube 306 has fluid therein at the locationbetween the ultrasonic transducers 866 and 868, the ultrasonicvibrations will easily pass therethrough. On the other hand, if there isair in the outlet tube 306 at the location between the ultrasonictransducers 866 and 868, the ultrasonic vibrations will become greatlyattenuated and a much lower signal (two orders of magnitude lower) willbe detected.

A simplified overview of the operation of the entire pump system isillustrated in FIG. 107. A pump control system 886 is used to drive apower module 888, which in turn operates a pump 890. An encoder 892 isused to supply position information from the power module 888, whichposition information will indicate both the position of the pump 890(which in the present system is a piston-type pump located in theassembled cassette 302) and the amount of fluid pumped by the pump 890.The pump 890 pumps fluid from a fluid input through a pressuretransducer 894, and then through an ultrasonic air-in-line detector(AILD) 896 to a fluid output.

The encoder 892 provides an encoder output which is supplied to the pumpcontrol system 886 as a feedback signal. The pressure transducer 894provides a pressure output signal which is supplied to the pump controlsystem 886 for use in monitoring the pressure to detect an occluded linesituation. The AILD scheme used by the system of the present inventionhas two additional components, namely an AILD monitoring system 898 anda self test system 900. The ultrasonic AILD 896 supplies two signals tothe AILD monitoring system 898 and the self test system 900,specifically an interrupt signal and an AILD output signal. The natureof these two signals will become evident in the detailed discussionbelow.

The AILD monitoring system 898 is used to monitor the signals from theultrasonic AILD 896 to determine when air is in the fluid line. Moreparticularly, in the preferred embodiment the AILD monitoring system 898will be used to determine when a predetermined amount of air has passedthrough the line during the passage past the sensor of a particularquantity of pumped volume, which is called a volume window. When therehas been the predetermined amount of air in the fluid line during avolume window, an alarm will be sounded and the pumping of fluid will beceased. The concept of a volume window will be explained in detailbelow.

The self-test system 900 is used periodically to ensure that theultrasonic AILD 896 is functioning properly, and not giving falseassurances that there is fluid in the line when in fact air is in theline. The self-test system 900 functions by providing a test signal tothe ultrasonic AILD 896 causing it to operate during the self-test at afrequency which is not resonant. Thus, during the self-test procedure asignal should be generated which would otherwise indicate the presenceof air in the line. The generation of an air-in-line signal during theself-test procedure is an indication that the system is functioningproperly.

Referring next to FIG. 108, a clock having an operating frequency of3.072 MHz is used to drive the transmitter circuitry. The clock signalis supplied to a duty cycle generator 902, which generates a 166 μS lowpulse once every 1.33 mS (750 Hz). The 750 Hz rate is chosen to besufficiently often to detect a bubble at even the highest flow ratesthrough the outlet tube 306. The pulse is thus on a one-eighth dutycycle, which is used to conserve power in the system. The output pulsetrain of the duty cycle generator 902 is supplied as the inhibit inputto a voltage controlled oscillator (VCO) 904.

The output pulse train from the duty cycle generator 902 is alsosupplied as an input to a inverter 906. The output of the inverter 906is supplied to one side of a resistor 908, the other side of which isconnected to the VCO in pin of the VCO 904. A capacitor 910 is connectedon one side to the VCO in pin of the VCO 904, and on the other side toground. The resistor 908 and the capacitor 910 act as an RC integratorto integrate the inverted inhibit waveform. The inhibit waveformsupplied to the VCO 904 and the VCO input waveform supplied to the VCO904 are illustrated in FIG. 111.

The output of the VCO 904 will be a variable frequency sweeping from alower frequency to a higher frequency. The resonant frequency of theultrasonic transducers 866 and 868 is nominally 1.8 MHz. Unless theultrasonic transducers 866 and 868 are high precision devices, the exactresonant frequencies may vary somewhat, and may also vary slightly overa period of time. Thus, the VCO 904 is used to generate a variablefrequency sweeping from, for example, 1.3 MHz to 2.3 Mhz, a sweep whichis certain to include the resonant frequency of the ultrasonictransducers 866 and 868. This sweep will be generated on the one-eightduty cycle as shown in FIG. 111, thereby conserving energy required bythe VCO 904 while repeating the sweep on a 750 Hz frequency to detectbubbles even at the fastest flow rate.

Referring again to FIG. 108, the output of the VCO 904 is supplied toone input side of three single-pole, double-throw switches 912A, 912B,and 912C. The other input side of these switches 912A, 912B, and 912C isconnected directly to the 3.072 MHZ clock. The outputs of the switches912A, 912B, and 912C may thus be switched between the output of the VCO904 and the 3.072 MHz clock. Normally, the outputs of the switches 912A,912B, and 912C are connected to the output of the VCO 904. Only when theself-test is to be performed are the outputs of the switches 912A, 912B,and 912C connected to the 3.072 MHz clock signal.

The outputs of the switches 912A, 912B, and 912C are connected to theinput side of three inverters 914A, 914B, and 914C, respectively. Theoutputs of the three inverters 914A, 914B, and 914C are connected to theinputs of three buffers 916 A, 916B, and 916C, respectively, The threebuffers 916A, 916B, and 916C are each contained on one of the printedcircuit boards 884 (FIG. 87) used for the three channels. The outputs ofthe three buffers are connected to one side of three (one for eachchannel) ultrasonic transducers 866A, 866B, and 866C, respectively. Theother sides of the three ultrasonic transducers 866A, 866B, and 866C aregrounded.

Referring again to FIG. 111 in addition to FIG. 108, it is apparent thatthe three ultrasonic transducers 866A, 866B, and 866C will be excitedwith a sweeping frequency from 1.3 MHz to 2.3 MHz on a one-eighth dutycycle once every 1.33 mS (750 Hz). This is frequent enough so that evenat the maximum pumping rate only a small amount of fluid can pass pastthe position of the ultrasonic transducer pairs between sequentialultrasonic transmissions. The one-eighth duty cycle conserves energyused by both the VCO 904 and the three ultrasonic transducers 866A,866B, and 866C.

FIG. 109 illustrates the receiver circuitry used for one of the threechannels, with the other two channels using identical circuitry. Thereceiving transducer for the first channel is the ultrasonic transducer868A, the output of which is supplied to a cascode preamplifier 918A.The output of the cascode preamplifier 918A will be a signal increasingin strength at the resonant frequency when fluid is present, and thushaving a triangular envelope as illustrated in FIG. 111. The output ofthe cascode preamplifier 918A is supplied to a detector/rectifier 920A,the output of which is the rectifier output shown in FIG. 111.

The output of the detector/rectifier 920A is supplied to a firstcomparator 922A, which produces the waveform shown in FIG. 111 when theenvelope from the detector/rectifier 920A is below a threshold. Theoutput from the first comparator 922A is supplied to an RC Timer/seconddetector 924A, which integrates the output from the first comparator922A, as shown in FIG. 111. The integrated output is reset each timethere is a signal from the ultrasonic transducer 868A which is over thethreshold of the first comparator 922A. When there is air in the line,the integrated signal will not be reset, causing it to reach thethreshold of the second comparator. At this point, the output of thesensor A circuitry will go low.

In summary, when there is fluid in the outlet tube 306, the ultrasonictransducer 868A will receive a strong signal, and a high sensor A outputwill be given indicating the presence of fluid in the outlet tube 306.When there is air in the outlet tube 306, the ultrasonic transducer 868Awill receive a weak signal, and a low sensor A output will be givenindicating the presence of air in the outlet tube 306. Circuitryidentical to that shown in FIG. 109 is used for the other two channels.

Referring now to FIG. 110, additional processing circuitry used toobtain the two signals used by the AILD monitoring system 898 and theself-test system 900 of FIG. 107 is illustrated. The sensor A output issupplied to the D input of a latch 924A, the output of which is AILDoutput A. AILD output A will be low when fluid is in the outlet tube306, and high when air is in the outlet tube 306. AILD output A issupplied to an edge detector 926A (one possible circuit for which isillustrated), the output of which will be a Channel A edge signalindicating either a rising or a falling edge in AILD output A. Thus,whenever an air/fluid interface is detected, the edge detector 928 Awill produce an output signal.

The other two channels use similar circuitry to produce correspondingsignals. Thus, an AILD output B and a Channel B edge signal will beproduced by circuitry for Channel B. Similarly, an AILD output C and aChannel C edge signal will be produced by circuitry for Channel C.

The Channel A edge signal, the Channel B edge signal, and the Channel Cedge signal are supplied to an OR gate 930. The output of the OR gate930 will be high if any of the three inputs are high. Thus, whenever anedge is present in any of AILD output A, AILD output B, or AILD outputC, the output of the OR gate 930 will be high. The output of the OR gate930 is used to latch a latch 932 high, to generate an interrupt signalAILD IRQ. This interrupt signal indicates that a change in state of oneof AILD output A, AILD output B, or AILD output C has occurred.

Thus, the circuitry of FIG. 110 will generate two signals. The firstsignal indicates the presence of air or fluid in the outlet tube 306 ofa channel, and the second signal indicates a change in state in one ofthe three channels. The first signal thus comprises the signals AILDoutput A, AILD output B, or AILD output C, while the second signal isthe interrupt signal AILD IRQ. For the rest of the explanation of theoperation of the system, only the first channel (channel A) will bediscussed. The operations of the other two channels (channels B and C)are identical in operation to the operation of the first channel.

Prior to a discussion of the operation of the AILD monitoring system898, the concept of controlling the amount of air which may be pumpedinto a patient must first be discussed. First, it must be realized thatit is not harmful to pump a small amount of air intravenously into manypatients; in fact, many medications are not degassed and will containsome amount of air therein, which air may form small bubbles. Only a fewpatients can tolerate no air introduced into their venous systems, suchas neonates, pediatrics, and those patients having septal defects. Otherthan when infusing fluid into such patients, or performing anintra-arterial infusion, the introduction of a very small quantities ofair is not believed to be particularly harmful. The attending physicianalso has the option of using air eliminating filters in such patients.

The other problem faced in monitoring air in the fluid line to a patientis that it is undesirable to have too many alarms due to extremely smallamounts of air being infused into most patients. The professional staffin most hospitals tend to view such frequent alarms as nuisance alarmswhich are undesirable and serve no useful purpose. Thus, the realpurpose of an AILD system is to prevent unduly large, potentiallydangerous quantities of air from being pumped into a patient. It istherefore necessary for the AILD system to allow some air past itwithout alarming, since a failure to do so could result in a largenumber of nuisance alarms. The AILD system must always alarm at somethreshold, which has been selected as being high enough to preventnuisance alarms but yet low enough to uniformly sense an amount of airpresenting even a remote threat to the health of the patient. Thisobjective may be implemented by using the concept of windowing.

The concept of windowing is when the passage of air bubbles in theimmediately previous preset volume of fluid is remembered. Such a windowis used to monitor the amount of air which may be included in a the mostrecent amount of a particular volume pumped to the patient. For example,in the last 2 milliliters of volume pumped, less than 100 microliters ofair may be present without an alarm. As soon as 100 microliters of airis present in the last 2 milliliters of volume pumped, an alarm is to begiven. This may be seen as a "forgetting" factor wherein all air bubblespumped prior to the last 2 milliliters of volume pumped are forgotten bythe system.

Such a volume window allows a particular amount of air less than apredetermined volume to be pumped within the last predetermined windowvolume. In the preferred embodiment the predetermined volume isone-twentieth (0.05) of the window volume. The window volume may be upto three milliliters, which is less than the volume of the deliverytubing 303. Thus, for a 50 microliter predetermined volume the windowvolume would be 1 milliliter, and for a 100 microliter predeterminedvolume the window volume would be 2 milliliters.

In some circumstances a larger predetermined volume may be appropriate.In any event, it will be realized by those skilled 5 in the art that theproportion could be varied from perhaps one-one hundredth (with ansubstantial increase in the number of nuisance alarms) to perhaps as lowas one-sixth (with special precautions such as the use of an air filterbeing taken). The preferred proportion is approximately one-twentieth.

The windowing scheme used by the present invention uses two pieces ofinformation to determine whether the system has just pumped air or fluidin the immediately preceding time period since the next previous update.First, the sensor will detect whether there is currently air in the lineat the sensor location. The second piece of information is whether atthe immediately preceding time period at which information was beinggathered there was air or fluid at the sensor location. This secondinformation will thus indicate whether the bubble currently sensed is acontinuation of a bubble started earlier, or the leading edge of a newbubble. Thus whether the system has just been pumping fluid or air inthe immediately preceding time interval since the last update may bedetermined.

For example, if the current sensor reading indicates air in the line andthe immediately previous reading was also air, then there is at thepresent time a continuing air bubble present in the fluid line. If thecurrent sensor reading indicates air in the line and the immediatelyprevious reading was fluid, then the leading edge of an air bubble hasbeen sensed. If current sensor reading indicates fluid in the line andthe immediately previous reading was air, then the trailing edge of anair bubble has been sensed. If current sensor reading indicates fluid inthe line and the immediately previous reading was also fluid, then thereis at the present time a continuing segment of fluid present in thefluid line.

The operation of the AILD monitoring system 898 may now be discussedwith reference to the flow chart of FIG. 112. The operation is acircuitous one, repeating at a high frequency, and beginning at block934. Since the system discussed herein is a three channel system, onlythe operation of the first channel (Channel A) will be discussed; theoperation of the other two channels (Channels B and C) is identical. Inblock 934 it is determined whether an interrupt signal AILD IRQ has beengenerated. If no interrupt signal has been generated, the operation goesto block 936. If an interrupt signal has been generated, the latch 932(FIG. 110) is reset by an AILD IRQ CLR signal on pin C. The operationwould then proceed to block 938.

In block 936 it is determined whether the end of a delivery stroke inthe pump 890 (FIG. 107) has been reached. If the end of a deliverystroke has not been reached, the operation returns to block 934. If theend of a delivery stroke has been reached, the operation would thenproceed to block 938. Thus, it is apparent that the chain of eventsbeginning at block 938 will be initiated either if an interrupt signalis generated or if the end of a delivery stroke has been reached.

In block 938 the AILD output is read; for channel A, AILD output A wouldbe read. Then, in block 940, the encoder output (for encoder A) is read.This will indicate how much volume has been pumped since the last timethe operation occurred. Then, in block 942, the pressure output (forchannel A) is read. This may be used to normalize the volume pumpedusing Boyle's law (P₁ *V₁ =P₂ *V₂). Then, in block 944, a determinationis made whether AILD output A indicates that there is currently air inthe line at the sensor location. This is the first piece of informationmentioned above, and it enables the system to divide into one of twobranches depending on the outcome of the determination.

If there is currently air in the portion of the fluid line where thesensor is located, the system moves to block 946; if there is currentlyno air in the portion of the fluid line where the sensor is located, thesystem moves to block 948. The operations which follow block 946 thusfollow a determination that there is currently air in the tubing at thesensor location. Similarly, the operations which follow block 948 followa determination that there is currently no air in the tubing at thesensor location. In each case, the second piece of information, whetherat the immediately preceding time period at which information wasgathered there was air or fluid at the sensor location, must next beevaluated for each of the two possibilities in blocks 946 and 948.

First in block 946, a determination is made as to whether at theimmediately preceding cycle during which information was gathered therewas air or fluid at the sensor location. If the determination is madethat there was air in the tubing at the sensor location at the time ofthis next previous update, the system will move to block 950. If, on theother hand the determination is made that there was no air in the tubingat the sensor location at the time of this next previous update, thesystem will move to block 952.

Thus, the block 950 will be reached if the current sensor readingindicates air in the line and the immediately previous reading alsoindicated the presence of air in the line. In this case, there is an airbubble in the line which existed at the next previous sensor reading andwhich still exists. Thus, in the block 950 the additional volume of theair bubble between the time of the next previous sensor reading and thepresent time is computed. Then, in block 954, the window is updated tocalculate how much of the volume window is currently air bubbles.

In block 954 the additional volume of the air bubble between the time ofthe next previous sensor reading and the present time is added to thevolume of air contained in the volume window, and air bubbles now beyondthe back edge of the window are subtracted from the volume of aircontained in the volume window. In this manner, the volume window isupdated to determine the volume of gas bubbles in the last volume windowvolume to pass through the ultrasonic sensor.

The sequence would then move to block 960, in which a determination ismade as to whether the portion of the volume window which is air bubblesexceeds the predetermined maximum. If the portion of the volume windowwhich is air bubbles exceeds the predetermined maximum, the system movesto block 962, and an alarm is sounded and the pumping of fluid by thesystem will be ceased. If the portion of the volume window which is airbubbles does not exceed the predetermined maximum, the system moves backto block 934.

The block 952 will be reached if the current sensor reading indicatesair in the line and the immediately previous reading indicated thepresence of fluid in the line. In this case, there is an air bubble inthe line which did not exist at the next previous sensor reading, butrather has just started (the starting edge of the bubble has beendetected). Thus, in the block 952 the additional volume of the fluidbetween the time of the next previous sensor reading up to the beginningof the bubble is computed. Then, in block 956, the window is updated tocalculate how much of the volume window is air bubbles.

In the preferred embodiment, an allowance is made for the fact that anair bubble must be at least a minimum size before it can be detected.Thus, when an air bubble is first detected, it is assumed that it is atleast this minimum bubble size up to this point. The minimum bubble sizeused in the preferred embodiment is 6 microliters.

In block 956, since there is fluid between the time of the next previoussensor reading and the present time, only the minimum bubble size of 6microliters is added to the volume of air contained in the volumewindow, and air bubbles now beyond the back edge of the window aresubtracted from the volume of air contained in the volume window. Inthis manner, the volume window is updated to determine the volume of airbubbles in the last volume window volume to pass through the ultrasonicsensor.

In block 958, the window information is switched to indicate that thepresent information, soon to become the next previous update, indicatesthe presence of air. Thus, the next time the system moves through theloop, the second piece of information will indicate that at the previousupdate, there was air present in the tubing.

The sequence would then move to block 960, in which a determination ismade as to whether the portion of the volume window which is air bubblesexceeds the predetermined maximum. If the portion of the volume windowwhich is air bubbles exceeds the predetermined maximum, the system movesto block 962, and an alarm is sounded and the pumping of fluid by thesystem will be ceased. If the portion of the volume window which is airbubbles does not exceed the predetermined maximum, the system moves backto block 934.

Alternatively, if there is presently no air in the line in block 944,the system would have moved to block 948. In block 948, a determinationis made as to whether at the immediately preceding time period at whichinformation was gathered there was air or fluid at the sensor location.If the determination is made that there was air in the tubing at thesensor location at the time of this next previous update, the systemwill move to block 964. If, on the other hand the determination is madethat there was no air in the tubing at the sensor location at the timeof this next previous update, the system will move to block 966.

Thus, the block 964 will be reached if the current sensor readingindicates a lack of air presently in the line, but the immediatelyprevious reading indicated the presence of air in the line. In thiscase, there was an air bubble in the line which existed at the nextprevious sensor reading, but which bubble ended (the trailing edge of anair bubble has been detected). Thus, in the block 964 the additionalvolume of the gas bubble between the time of the next previous sensorreading and its ending point at the present time is computed. Then, inblock 968, the window is updated to calculate how much of the volumewindow is air bubbles.

In block 968 the additional volume of the air bubble from the time ofthe next previous sensor reading which ended at the present time isadded to the volume of air contained in the volume window, and airbubbles now beyond the back edge of the window are subtracted from thevolume of air contained in the volume window. In this manner, the volumewindow is updated to determine the volume of air bubbles in the lastvolume window volume to pass through the ultrasonic sensor.

In block 972, the window information is switched to indicate that thepresent information, soon to become the next previous update, indicatesthe absence of air. Thus, the next time the system moves through theloop, the second piece of information will indicate that at the previousupdate, there was no air present in the tubing.

The sequence would then move to block 960, in which a determination ismade as to whether the portion of the volume window which is air bubblesexceeds the predetermined maximum. If the portion of the volume windowwhich is air bubbles exceeds the predetermined maximum, the system movesto block 962, and an alarm is sounded and the pumping of fluid by thesystem will be ceased. If the portion of the volume window which is airbubbles does not exceed the predetermined maximum, the system moves backto block 934.

The block 966 will be reached if the current sensor reading indicates noair in the line and the immediately previous reading also indicated thepresence of fluid in the line. In this case, there is and has been fluidin the line from the time of the immediately previous reading to thepresent. Thus, in the block 966 the additional volume of the fluidbetween the time of the next previous sensor reading up to the beginningof the bubble is computed. Then, in block 970, the window is updated tocalculate how much of the volume window is air bubbles.

In block 970, since there is fluid between the time of the next previoussensor reading and the present time, no additional volume of air isadded to the volume of air contained in the volume window, and airbubbles now beyond the back edge of the window are subtracted from thevolume of air contained in the volume window. In this manner, the volumewindow is updated to determine the volume of air bubbles in the lastvolume window volume to pass through the ultrasonic sensor.

The sequence would then move to block 960, in which a determination ismade as to whether the portion of the volume window which is air bubblesexceeds the predetermined maximum. If the portion of the volume windowwhich is air bubbles exceeds the predetermined maximum, the system movesto block 962, and an alarm is sounded and the pumping of fluid by thesystem will be ceased. If the portion of the volume window which is airbubbles does not exceed the predetermined maximum, the system moves backto block 934.

It must be realized that the flow chart of FIG. 112 represents a highlysimplified example of how the system may be implemented to perform thewindowing function. Those skilled in the art will immediately understandthe principles behind this operation, and will be able to implement itin a variety of manners. The advantages of the technique areself-evident--the pumping of an excessive amount of air into a patientis avoided, while the occurrence of nuisance alarms is avoided.

Turning now to FIG. 113, the operation of the self-test system isillustrated in a simplified manner. The self-test is performed in thepreferred embodiment once per cycle after it has been determined thatthe end of a delivery cycle has been reached, assuming that the portionof the volume window which is air bubbles did not exceed thepredetermined maximum. The initial determination is made in block 980whether the end of a delivery cycle has been reached. If the end of adelivery cycle has been reached, the system moves to block 982. If theend of a delivery cycle has not been reached, the system moves back tothe beginning of block 980.

A determination is made in block 982 whether AILD output A whether thatthere is currently air in the line at the sensor location. If there isair in the line, the self-test may not be run, and the system moves backto the beginning of block 980. If there is not currently air in thesensor, the system moves to block 984.

In block 984, the frequency supplied to the ultrasonic transducer 866Ais changed to a non-resonant frequency. (Referring briefly to FIG. 108,the switch 912A would be switched to connect the 3.072 MHz clock to theinverter 914A.) This frequency is far enough from the resonant frequencythat the ultrasonic transducer 868A will not resonate. At this point,the AILD output A should indicate air and an interrupt signal shouldquickly be generated. If a signal is generated by the ultrasonictransducer 868B, this would indicate that there is a failure in theultrasonic transducer 868B or in the associated electronics.

Accordingly, in block 986 if the interrupt signal does not appear withina preset time it will be apparent that there is an error, and the AILDfault signal 987 will be sounded and the pumping operation ceased. Ifthe interrupt signal appears within the preset time, it is an indicationthat the system is functioning properly, and system will move on toblock 988. In block 988, the frequency supplied to the ultrasonictransducer 866A is changed back to the periodic resonant frequencyencompassing sweep. (Referring briefly to FIG. 108, the switch 912Awould be switched to connect the output of the VCO 904 to the inverter914A.) The system will move back to the beginning of block 980, and thesequence will be repeated.

Through the above discussion of the entire system, it will beappreciated that the present invention provides an ultrasonicair-in-line detection sensor for use with the outlet tubing from acassette in which the tubing is automatically loaded into the properposition in the sensor when the cassette is installed on a main pumpunit. The system of the present invention thus loads the tubing into thesensor, in the proper position, with no more effort required than theeffort to load the cassette itself onto the main pump unit. The tubingis thereby loaded correctly into the sensor in a highly repeatablemanner whenever the cassette is installed.

Once the tubing has been properly loaded into the sensor, it is retainedin the sensor in a manner making it impossible for the tubing to movewith respect to the sensor. The tubing is thus both properly loadedinitially into the sensor, and retained in its proper position in thesensor to prevent false signals due to movement of the tubing in thesensor. In addition, the tubing is automatically removed from the sensorwhen the cassette is removed from the main pump unit without requiringany additional steps to be performed.

Despite the inclusion of the aforesaid features, the system of thepresent invention utilizes a minimum number of parts, all of which partsare of inexpensive construction, yet which afford the assembled cassettea high degree of accuracy. The system of the present invention istherefore able to compete economically with known competing systems, andit provides an ease of use rivaling the best of competing systems. Thesystem accomplishes all these objects in a manner which retains andenhances the advantages of reliability, durability, and safety ofoperation, without incurring any relative disadvantage.

Although an exemplary embodiment of the present invention has been shownand described, it will be apparent to those having ordinary skill in theart that a number of changes, modifications, or alterations to theinvention as described herein may be made, none of which depart from thespirit of the present invention. All such changes, modifications, andalterations should therefore be seen as within the scope of the presentinvention.

What is claimed is:
 1. A system for automatically loading a segment oftubing extending from the bottom of a disposable, fluid-pumping cassetteinto engagement with an ultrasonic sensor as the cassette is installedonto a main pump unit, comprising:a main pump unit chassis definingthereunder a location into which said cassette may be installed; asensor housing mounted on said main pump unit chassis below saidlocation into which said cassette may be installed, said sensor housinghaving a vertically oriented slot located in the front thereof forreceiving said segment of tubing, said sensor housing being hollow; anultrasonic transmitter located in said sensor housing on one side ofsaid slot; an ultrasonic receiver located in said sensor housing on theother side of said slot; a recess located in the bottom of said sensorhousing on both sides of said slot in said sensor housing; a hollowcylindrical tubing adapter installed on said segment of tubing extendingfrom the bottom of said cassette, the top end of said tubing adapterbeing tapered, said tubing adapter being spaced away from the bottom ofsaid cassette sufficiently far so that as said cassette is inserted intosaid location defined by said main pump unit chassis said tapered topend of said tubing adapter will engage the bottom of said sensorhousing, said tapered top end of said tubing adapter engaging saidrecess in the bottom of said sensor housing to draw said segment oftubing extending from the bottom of said cassette into said slot in saidsensor housing when said cassette is inserted into said position definedby said main pump unit chassis.
 2. A system as defined in claim 1,additionally comprising:an inclined ramp located on the bottom and inthe front of the ultrasonic sensor housing on each side of the slot,with the ramps being inclined toward said recess in the bottom of saidultrasonic sensor housing to urge said tapered top end of said tubingadapter into engagement with said recess in the bottom of said sensorhousing.
 3. A system as defined in claim 1, wherein said slot has afunnel-shaped entrance to allow said segment of tubing to be directedinto said slot.
 4. A system as defined in claim 1, wherein said slot isnarrower than the outer diameter of said segment of tubing.
 5. A systemas defined in claim 1, wherein said ultrasonic transmitter is adhesivelymounted to the interior of said sensor housing on said one side of saidslot, and said ultrasonic receiver is adhesively mounted to the interiorof said sensor housing on said other side of said slot.
 6. A system asdefined in claim 1, wherein said sensor housing comprises:an uppersensor housing which is rectangular in configuration and has avertically oriented opening in the front thereof forming the upperportion of said slot, said upper housing being open on the bottomthereof, said upper housing defining first and second areas on theinterior thereof on each side of said opening, a third area beingdefined by that portion of the interior of said upper housing into whichsaid opening does not protrude; and a lower sensor housing disposedunder said upper sensor housing, said lower sensor housing having anopening in the front thereof forming the lower portion of said slot,said lower sensor housing sealing the open areas of said upper sensorhousing.
 7. A system as defined in claim 6, wherein said ultrasonictransmitter is located in said first area against the interior wall ofsaid first area facing said opening in said upper sensor housing, andwherein said ultrasonic receiver is located in said second area againstthe interior wall of said second area facing said opening in said uppersensor housing.
 8. A system as defined in claim 7, additionallycomprising:a first foam segment located between said ultrasonictransmitter and the interior wall of said first area opposite theinterior wall of said first area facing said opening in said uppersensor housing; and a second foam segment located between saidultrasonic receiver and the interior wall of said second area oppositethe interior wall of said second area facing said opening in said uppersensor housing.
 9. A system for automatically loading a segment oftubing extending from the bottom of a disposable, fluid-pumping cassetteinto engagement with an ultrasonic sensor as the cassette is installedonto a main pump unit, comprising:a main pump unit chassis definingthereunder a location into which said cassette may be installed; asensor housing mounted on said main pump unit chassis below saidlocation into which said cassette may be installed, said sensor housinghaving a vertically oriented slot located in the front thereof forreceiving said segment of tubing, wherein said slot is narrower than theouter diameter of said segment of tubing, said sensor housing beinghollow; an ultrasonic transmitter located in said sensor housing on oneside of said slot, wherein said ultrasonic transmitter is adhesivelymounted to the interior of said sensor housing on said one side of saidslot; an ultrasonic receiver located in said sensor housing on the otherside of said slot, wherein said ultrasonic receiver is adhesivelymounted to the interior of said sensor housing on said other side ofsaid slot; a recess located in the bottom of said sensor housing on bothsides of said slot in said sensor housing; an inclined ramp located onthe bottom and in the front of said ultrasonic sensor housing on eachside of the slot, with the ramps being inclined toward said recess inthe bottom of the ultrasonic sensor housing; a hollow cylindrical tubingadapter installed on said segment of tubing extending from the bottom ofsaid cassette, the top end of said tubing adapter being tapered, saidtubing adapter being spaced away from the bottom of said cassettesufficiently far so that as said cassette is inserted into said locationdefined by said main pump unit chassis said tapered top end of saidtubing adapter will engage said ramps of said sensor housing, saidtapered top end of said tubing adapter sliding along said ramps intoengagement with said recess in the bottom of said sensor housing to drawsaid segment of tubing extending from the bottom of said cassette intosaid slot in said sensor housing when said cassette is inserted intosaid position defined by said main pump unit chassis.
 10. A system forautomatically loading a segment of tubing extending from the bottom of adisposable, fluid-pumping cassette into engagement with an ultrasonicsensor as the cassette is installed onto a main pump unit, comprising:amain pump unit chassis defining thereunder a location into which saidcassette may be installed; a sensor housing mounted on said main pumpunit chassis below said location into which said cassette may beinstalled, said sensor housing having a pair of arms extending towardsthe front, said arms defining a vertically oriented slot therebetweenfor receiving said segment of tubing; an ultrasonic transmitter locatedin one of said arms, said ultrasonic transmitter directed toward saidslot; an ultrasonic receiver located in the other of said arms, saidultrasonic receiver directed toward said slot; a recess located in thebottom of said sensor housing on both sides of said slot in said sensorhousing; a hollow cylindrical tubing adapter installed on said segmentof tubing extending from the bottom of said cassette, the top end ofsaid tubing adapter being tapered, said tubing adapter being spaced awayfrom the bottom of said cassette sufficiently far so that as saidcassette is inserted into said location defined by said main pump unitchassis said tapered top end of said tubing adapter will engage thebottom of said sensor housing, said tapered top end of said tubingadapter engaging said recess in the bottom of said sensor housing todraw said segment of tubing extending from the bottom of said cassetteinto said slot in said sensor housing when said cassette is insertedinto said position defined by said main pump unit chassis.
 11. A systemas defined in claim 10, additionally comprising:an inclined ramp locatedon the bottom and in the front of said ultrasonic sensor housing on theend of each arm thereof, with the ramps being inclined toward saidrecess in the bottom of the ultrasonic sensor housing.
 12. A system forautomatically loading a segment of tubing extending from a disposable,fluid-pumping cassette into engagement with an ultrasonic sensor as thecassette is installed onto a main pump unit, comprising:a main pump unitchassis defining a location into which said cassette may be installed; asensor housing mounted on said main pump unit chassis adjacent saidlocation into which said cassette may be installed, said sensor housinghaving a slot located therein for receiving said segment of tubing, saidsensor housing being hollow; an ultrasonic transmitter located in saidsensor housing on one side of said slot; an ultrasonic receiver locatedin said sensor housing on the other side of said slot; a recess locatedin the side of said sensor housing facing away from said location intowhich said cassette may be installed, said recess being located on bothsides of said slot in said sensor housing; a hollow cylindrical tubingadapter installed on said segment of tubing extending from saidcassette, the end of said tubing adapter nearest said cassette beingtapered, said tubing adapter being spaced away from said cassette sothat as said cassette is inserted into said location defined by saidmain pump unit chassis said tapered end of said tubing adapter willengage the side of said sensor housing facing away from said locationinto which said cassette may be installed, said tapered end of saidtubing adapter engaging said recess in said sensor housing to draw saidsegment of tubing extending from said cassette into said slot in saidsensor housing when said cassette is inserted into said position definedby said main pump unit chassis.
 13. A system as defined in claim 12,additionally comprising:an inclined ramp located on the side of saidsensor housing facing away from said location into which said cassettemay be installed bottom and in the front of the ultrasonic sensorhousing on each side of the slot, with the ramps being inclined towardsaid recess in said ultrasonic sensor housing to urge said tapered endof s id tubing adapter into engagement with said recess in said sensorhousing.
 14. A system for automatically loading a segment of tubingextending from the bottom of a disposable, fluid-pumping cassette intoengagement with a sensor as the cassette is installed onto a main pumpunit, comprising:a main pump unit chassis defining thereunder a locationinto which said cassette may be installed; a sensor housing mounted onsaid main pump unit chassis below said location into which said cassettemay be installed, said sensor housing having a vertically oriented slotlocated in the front thereof for receiving said segment of tubing; arecess located in the bottom of said sensor housing on both sides ofsaid slot in said sensor housing; a hollow cylindrical tubing adapterinstalled on said segment of tubing extending from the bottom of saidcassette, the top end of said tubing adapter being tapered, said taperedtop end of said tubing adapter for engaging said recess in the bottom ofsaid sensor housing when said cassette is inserted into said positiondefined by said main pump unit chassis.
 15. A system as defined in claim14, additionally comprising:an inclined ramp located on the bottom andin the front of the ultrasonic sensor housing on each side of the slot,with the ramps being inclined toward said recess in the bottom of saidultrasonic sensor housing to urge said tapered top end of said tubingadapter into engagement with said recess in the bottom of said sensorhousing.
 16. A method of automatically loading a segment of tubingextending from the bottom of a disposable, fluid-pumping cassette intoengagement with an ultrasonic sensor as the cassette is installed onto amain pump unit, comprising:defining a location into which said cassettemay be installed under a main pump unit chassis; mounting a sensorhousing on said main pump unit chassis below said location into whichsaid cassette may be installed, said sensor housing having a verticallyoriented slot located in the front thereof for receiving said segment oftubing, said sensor housing being hollow; locating an ultrasonictransmitter in said sensor housing on one side of said slot; locating anultrasonic receiver in said sensor housing on the other side of saidslot; situating a recess in the bottom of said sensor housing on bothsides of said slot in said sensor housing; installing a hollowcylindrical tubing adapter on said segment of tubing extending from thebottom of said cassette, the top end of said tubing adapter beingtapered, said tubing adapter being spaced away from the bottom of saidcassette sufficiently far so that as said cassette is inserted into saidlocation defined by said main pump unit chassis said tapered top end ofsaid tubing adapter will engage the bottom of said sensor housing, saidtapered top end of said tubing adapter engaging said recess in thebottom of said sensor housing to draw said segment of tubing extendingfrom the bottom of said cassette into said slot in said sensor housingwhen said cassette is inserted into said position defined by said mainpump unit chassis.